SB    ID 


CALIFORWJA 


EAHTH 

SCIENCE* 
UBRARY 


THE  CAUSE  OF  EARTHQUAKES,   MOUNTAIN   FORMATION 

AND  KINDRED  PHENOMENA  CONNECTED  WITH 

THE  PHYSICS  OF  THE  EARTH 


BY  T.  J.  J.   SEE,  A.M.,  Lx.M.,  Sc.M.   (Missou.),  A.M.,  Pn.D.   (BEROL.) 


Reprinted  from 

PROCEEDINGS  OF  THE  AMERICAN  PHILOSOPHICAL  SOCIETY 
VOL.  XLV.   1907 


; 


THE  CAUSE  OF  EARTHQUAKES,  MOUNTAIN  FORMA- 
TION AND  KINDRED  PHENOMENA  CONNECTED 
WITH  THE  PHYSICS  OF  THE  EARTH. 

BY  T.  J.  J.  SEE,  A.M.,   Lx.M.,  Sc.M.  (Missou.),  A.M.,  PH.D.  (BEROL.), 

PROFESSOR  OF  MATHEMATICS,  U.  S.  NAVY,  IN  CHARGE  OF  THE  NAVAL 
OBSERVATORY,  MARE  ISLAND,  CALIFORNIA. 


Reprinted  from  Proceedings  American  Philosophical  Society,    Vol.  xlv,^  1906. 


THE  CAUSE  OF  EARTHQUAKES,   MOUNTAIN   FORMA- 
TION AND  KINDRED  PHENOMENA  CONNECTED 
WITH  THE  PHYSICS   OF  THE  EARTH. 

BY  T.  J.  J.  SEE,  A.M.,  Lx.M.,  Sc.M.    (Missou.),  A.M.,   PH.D.    (BEROL.), 

PROFESSOR  OF  MATHEMATICS,   U.   S.   NAVY,   IN   CHARGE  OF  THE  NAVAL 
OBSERVATORY,  MARE  ISLAND,  CALIFORNIA. 

(Read  October  19,  1906.} 

I.     GENERAL  CONSIDERATIONS  ON  THE  CAUSE  OF  EARTHQUAKES. 
§  i.  Introduction. 

The  great  San  Francisco  earthquake  of  April  18,  1906,  presented 
certain  remarkable  characteristics  which  immediately  became  a  sub- 
ject of  investigation  on  the  part  of  men  of  science  resident  in  this 
part  of  the  United  States.  One  very  striking  feature  of  this  earth- 
quake was  the  conspicuous  rotatory  motion  of  the  earth  particle; 
and  another  was  the  long  duration  of  the  disturbance.  The  rotatory 
motion  appeared  so  remarkable  and  so  difficult  to  reconcile  with 
theories  very  generally  held  by  geologists  and  seismologists  that  it 
seemed  worth  while  to  make  a  somewhat  comprehensive  survey  of 
the  general  subject  of  earthquakes,  in  the  hope  of  reaching  a  better 
understanding  of  the  cause  of  these  phenomena.  And  as  the  details 
of  this  particular  earthquake  will  be  fully  treated  by  others,1  the 
result  of  the  present  inquiry2  into  the  physical  cause  of  earthquakes 

1  The   Committee   of   Investigation   appointed  by  the   Governor  of   Cali- 
fornia: Professors  A.  C.  Lawson,  George  Davidson,  A.  O.  Leuschner,  G.  K. 
Gilbert,   W.   W.   Campbell,   H.   F.   Ried,   J.    C.   Branner,   Chas.   Burkhalter. 
Investigations   are   being   made    also   by   Professor   Omori    of   the    Imperial 
University  of  Tokio,  Messrs.  Otto  Von  Geldern,  Luther  Wagoner,  and  Mr. 
Hoehl  of  the  American  Society  of  Civil  Engineers,  and  perhaps  by  others. 

2  Rear  Admiral  H.  H.  Rousseau,  U.   S.   Navy,  Chief  of  the  Bureau  of 
Yards  and  Docks,  has  read  this  paper  throughout,  and  made  a  number  of 
suggestions  which  proved  valuable.     The  independent  judgment  of  an  experi- 
enced engineer  was  felt  to  be  no  inconsiderable  advantage  in  weighing  some 
of  the  difficult  questions  here  treated,  and  my  most  cordial  acknowledgements 
are  due  to  Rear  Admiral  Rousseau  for  his  great  kindness. 

274 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  275 

and  other  related  phenomena  may  not  be  without  interest  to  investi- 
gators of  the  physics  of  the  earth. 

Almost  exactly  four  months  after  the  earthquake  of  April  18, 
namely,  August  16,  1906,  another,  much  more  terrible,  laid  waste 
Valparaiso  and  the  surrounding  cities  of  Chili,  producing  scenes  of 
desolation  which  are  rare — even  in  South  America.  The  scientific 
need  and  the  humanitarian  demand  for  an  investigation  of  the  cause 
of  these  disturbances  could,  therefore,  hardly  be  greater  than  it  is 
at  the  present  time.  But  if  it  be  said  that  the  researches  of  science 
are  powerless  to  stay  the  hand  of  the  destroyer,  and  only  the  laws 
of  these  terrible  phenomena  can  be  discovered,  yet  even  the  intelli- 
gent appreciation  of  natural  laws  may  greatly  mitigate  the  extent 
of  the  disaster  and  suffering  which  follow ;  and  on  both  humane  and 
scientific  grounds,  the  prospects  of  extending  the  domain  of  useful 
knowledge  furnish  a  high  inspiration  for  earnest  endeavor  to  pene- 
trate the  mystery  of  these  hidden  forces  of  nature,  which  so  long 
have  baffled  the  skill  of  philosophers. 

\Earthquakes  and  volcanoes  were  among  the  earliest  physical 
phenomena  to  receive  the  attention  of  the  ancients,  and  they  have 
always  occupied  a  prominent  place  in  natural  philosophy.  Although 
the  importance  of  the  subject  was  derived  originally  from  the  ter- 
rible disasters  which  these  mysterious  agencies  of  unknown  forces 
occasionally  inflict  upon  large  portions  of  mankind,  in  more  recent 
times  earthquakes  have  been  studied  also  as  about  the  only  available 
means  of  throwing  light  upon  the  physics  of  the  globe.  No  arti- 
ficial forces  at  the  command  of  the  experimenter  are  great  enough 
to  produce  vibrations  of  the  earth's  crust  or  to  transmit  them  through 
the  body  of  the  planet  when  once  established  in  the  surface  layers. 

But  notwithstanding  all  the  labor  and  research  which  has  been 
bestowed  upon  the  subject,  it  can  hardly  be  said  that  we  yet  have 
any  satisfactory  theory  of  the  cause  of  these  phenomena.  This  is 
the  more  regrettable,  because,  on  the  one  hand,  it  places  it  beyond 
the  power  of  science  to  predict  earthquakes,  or  even  to  foretell 
the  regions  of  their  occurrence,  which  might  afford  some  measure 
of  security  to  life  and  property;  while,  on  the  other,  it  leaves 
many  men  of  science  without  adequate  hope  that  the  true  cause  of 
these  phenomena  will  ever  be  discovered,  and  at  the  same  time  so 


276  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

completely  bewildered  by  a  multitude  of  unsatisfactory  theories  that 
the  progress  of  discovery  itself  is  seriously  embarrassed. 

There  will  naturally  be  those  who  doubt  the  existence  of  one 
common  and  universal  cause  of  earthquake  and  volcanic  phenomena. 
Nevertheless,  difficult  as  the  subject  is,  we  believe  that  such  a 
cause  exists,  and  that  it  is  capable  of  demonstration,  if  not  with 
mathematical  rigor  at  least  with  such  high  degree  of  probability1 
as  to  render  the  resulting  theory  practically  useful,  and  we  ask 
nothing  of  the  reader  except  a  careful  examination  of  the  facts 
as  interpreted  in  the  light  of  the  cause  assigned  in  this  paper. 
If  such  a  view,  associating  the  varied  phenomena  of  earthquakes 
and  volcanoes,  with  mountain  formation  and  the  development  of 
great  sea  waves,  under  one  common  cause,  renders  them  more  intel- 
ligible, and  enables  us  to  see  the  relations  of  all  the  observed  phe- 
nomena in  a  clearer  and  simpler  light,  there  will  be  presumptive 
evidence  of  the  truth  of  the  proposed  theory ;  and  the  probability  of 
its  correctness  will  increase  with  the  harmony  existing  among  all 
the  known  facts,  and  the  effectiveness  with  which  contradictions 
of  other  theories  may  be  established.  The  final  test  of  the  theory 
will  depend  upon  its  usefulness  in  the  advancement  of  discovery, 
so  as  to  harmonize  the  whole  body  of  earthquake  and  volcanic 
phenomena,  including  those  associated  with  the  origin  and  structure 
of  mountains,  the  observations  of  geodesy,  and  of  great  sea  waves, 
in  their  mutual  relations,  and  in  respect  to  the  undisturbed  parts 
of  our  globe.  If  the  theory  shall  meet  this  test  satisfactorily,  we  may 
feel  confident  that  it  assigns  the  true  cause  of  the  phenomena,  and 
within  certain  limits  the  resulting  laws  of  nature  may  be  used  to 
foretell  events  which  will  contribute  to  the  repose  and  safety  of 
mankind,  and  to  the  progress  and  usefulness  of  discovery  in  this 
interesting  branch  of  natural  philosophy. 

j§  2..  The  dynamical  cause  of  earthquakes  and  volcanoes  probably 

^he  unequivocal  proof  of  the  elevation  of  the  coast  at  Yakutat  Bay, 
Alaska,  Sept.  10-15,  1899,  seems  to  remove  the  last  trace  of  uncertainty  re- 
garding the  chief  function  of  earthquakes,  and  makes  the  demonstration  as 
rigorous  as  that  of  any  theorem  in  geometry.  See  the  important  memoir  of 
Tarr  and  Martin,  Bulletin  of  the  Geological  Society  of  America,  vol.  17,  May, 
1906.  Professor  Georee  Davidson,  President  of  the  Seismological  Society 
of  America,  kindly  called  my  attention  to  this  classic  work  after  the  present 
investigation  was  finished.  Note  added  December  12,  1906. 


Igo6.  SEE -THE  CAUSE  OF  EARTHQUAKES.  277 

depends  upon  the  explosive  pozver  of  steam  formed  within  or  just 
beneath  the  heated  rocks  of  the  earth's  crust  chiefly  by  the  leakage 
of  the  ocean  beds. 

Some  of  the  most  complicated  phenomena  in  nature  depend 
upon  the  simplest  and  most  obvious  of  causes,  but  there  are  several 
reasons  why  the  true  cause  often  proves  very  difficult  to  discover. 
On  the  one  hand  our  mental  operations  are  not  infrequently 
thwarted  by  conflicting  prejudices  and  contradictory  theories,  so 
that  attention  is  diverted  from  the  real  questions ;  and,  on  the  other, 
our  clearness  of  vision  and  power  of  intuition  are  blinded  by  the 
very  closeness  and  familiarity  of  the  true  cause,  which  is  least  sus- 
pected. Success  in  interpreting  nature  depends  upon  a  combination 
of  the  proper  elements  of  thought  into  one  simple  connected  view 
which  deals  not  with  details  but  with  the  general  tendencies.  In  the 
case  of  earthquakes  and  volcanoes  this  general  view  has  been  very 
difficult  to  obtain ;  and  with  the  growth  of  elaborate  scientific  inves- 
tigation and  classification  of  earthquakes  the  difficulty  has  increased 
rather  than  diminished.  For  attention  has  been  given  to  the 
attainment  of  high  accuracy  in  the  measurement  of  tremors  by 
seismographs  and  other  apparatus,  and  investigators  have  been  oc- 
cupied with  the  registration  and  discussion  of  the  details  of  phe- 
nomena rather  than  with  the  general  underlying  causes. 

We  shall  hereafter  examine  the  porosity  of  matter  and  the  prob- 
lem of  the  penetration  of  water  into  the  rocks  of  the  earth's  crust, 
both  from  the  experimental  and  historical  standpoints,  but  let  us 
first  consider  the  probable  state  of  the  internal  heat  of  the  earth. 
In  Astron.  Nach.,  No.  4053,  the  writer  has  shown  that  when  we 
consider  the  force  of  gravity  alone,  and  suppose  a  body  to  be  made 
up  of  gas  reduced  to  the  state  of  single  atoms,  over  one-half  of  the 
primordial  supply  of  heat  is  stored  up  within  the  condensing  mass, 
while  still  in  the  gaseous  stage ;  and  in  a  later  paper  on  the  rigidity 
of  the  heavenly  bodies  (A.  N.,  4104),  it  is  shown  that  circulation 
and  radiation  become  retarded  and  greatly  restricted  with  increasing 
density,  so  that  in  the  later  stages  of  the  development  of  a  mass  like 
the  earth,  much  more  than  one-half  of  the  heat  generated  is  retained 
within  the  mass  for  raising  the  temperature.  It  is  shown  that  all 
the  heat  of  our  earth  depending  on  gravitation  would  raise  the 


278  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

temperature  of  an  equal  mass  of  water  9954°  C. ;  and  as  decidedly 
more  than  half  of  it  is  still  retained  in  the  globe,  we  may  conclude 
that  the  internal  heat  of  the  earth  "is  ample  to  raise  the  whole  globe 
to  a  temperature  of  something  like  20,000°  or  25,000°  C.,  accord- 
ing to  the  average  specific  heat  of  the  earth's  matter.  If  radium  and 
other  related  elements  exist  within  the  earth  in  appreciable  quan- 
tities, the  amount  of  heat  stored  up,  as  Sir  G.  H.  Darwin  and 
others1  have  remarked,  may  be  vastly  greater  yet.  Now  it  is  recog- 
nized that  the  crust  or  cooled  layer  on  the  outside  of  our  planet  is 
extremely  thin,  and  we  know  that  the  temperature  increases  down- 
ward at  an  average  rate  of  something  like  i°  C.  for  each  30  metres 
of  descent.  This  accords  also  with  Lord  Kelvin's  calculations  on 
the  cooling  of  a  molten  globe,  carried  out  in  conformity  with 
Fourier's  Analytical  Theory  of  the  propagation  of  heat  in  solid 
bodies.2 

From  this  we  may  infer,  as  geologists  have  long  since  remarked, 
that,  even  without  the  penetration  of  steam,  molten  rock  would  be 
encountered  at  a  depth  of  decidedly  less  than  30  kilometres.  As  the 
percolation  of  hot  water  and  steam  appreciably  lowers  the  melting 
point  of  silicious  and  perhaps  other  rocks  (the  lavas  are  mainly 
silicates),  and  itself  develops  at  the  very  low  temperature  of  only 
100°  C.  under  atmospheric  pressure,  we  may  infer  that  it  would 
form  in  the  earth  at  a  depth  much  smaller  than  30  kms.  At  no  more 
than  10  or  15  kms.  under  the  ocean  beds  large  quantities  of  it  might 
be  produced  and  give  rise  to  imprisoned  forces  of  tremendous  power. 
Besides  it  would  rapidly  absorb  and  spread  in  the  hotter  layers  of 
rock  beneath,  just  as  in  the  case  of  gases  absorbed  in  hot  steel,  cited 
by  Tait  and  quoted  in  §  5.  That  this  absorption  actually  takes  place 
is  proved  by  the  vast  clouds  of  steam  given  off  by  melted  lava  after 
it  pours  from  a  volcano,  such  as  Vesuvius. 

We  are  thus  confronted  with  the  following  situation : 
\  The  internal  temperature  of  the  earth  is  extremely  high,  with 

1  Presidential  address  to  the  British  Association  for  the  Advancement  of 
Science,  Capetown,   1905;   also  a  very  recent  paper  presented  to  the  Royal 
Society,  April  5,  1906,  by  the  Hon.  R.  J.  Strutt,  F.R.S.,  reported  in  Nature 
of  May  17,  1906. 

2  "The  Secular  Cooling  of  the  Earth,"  Appendix  D,  Thomson  and  Tait's 
"Nat.  Phil." 


I9o6j 


SEE— THE  CAUSE  OF  EARTHQUAKES. 
FIG.  i. 


279 


Mt.   Pelee.      The  burning  cloud  of  December  16,   1902,  seen  from  the   sea. 
(From  the  Belgian  Astronomical  Society,  tenth  year.      Plate  V.) 

heated  rocks  quite  near  the  surface,  while  the  crust  is  fractured 
and  leaky  everywhere,  and  especially  where  the  depth  of  the  sea  is 
greatest.  The  sea  covers  three-fourths  of  the  earth's  surface,  and 
earthquakes  are  found  to  be  most  violent  -where  the  sea  is  deepest,  v 

PROC.  AMER.  PHIL.  SOC.,  XLV.  <84  R,  PRINTED  FEBRUARY  I9,  I9O7. 


280  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

, 

and  volcanoes  most  numerous  on  the  adjacent  shores.^  Could  then 
anything  be  more  probable  than  to  suppose  that  both  of  these  great 
natural  phenomena  depend  simply  and  wholly  upon  the  explosive 
power  of  steam  which  has  developed  in  the  heated  rock  of  the  earth's 
crust ? 

The  mere  statement  of  the  facts  seems  almost  enough  to  con- 
vince one  of  the  truth  of  this  theory.  But  in  view  of  the  wide 
differences  of  opinion  heretofore  prevailing  we  shall  examine  it  in 
detail,  and  we  believe  it  will  be  possible  to  show  that  no  contradiction 
can  be  established,  and  that  it  probably  is  the  correct  explanation 
of  the  mysterious  forces  which  have  so  long  baffled  investigators 
and  wrought  such  havoc  in  numerous  places  throughout  the  world. 

It  would  seem  that  the  obvious  fact  of  the  leaky  character  of 
the  sea  bottom,  covering  three-fourth's  of  the  earth,  with  great  in- 
ternal heat  everywhere  so  close  beneath  and  volcanoes  not  only 
abundant  on  the  shores  adjacent  to  the  deepest  seas,  but  pouring 
forth  vast  quantities  of  steam  when  in  eruption  long  ago  suggested 
and  apparently  ought  to  have  convinced  investigators  of  the  validity 
of  this  natural  and  simple  explanation.  But  it  appears  to  have  been 
generally  rejected,  owing  to  several  circumstances  which  did  not 
enable  investigators  to  obtain  the  proper  point  of  view.  On  the 
one  hand  there  were  traditional  theories  of  volcanoes  and  their 
relations  to  a  supposed  liquid  or  molten  globe;  and  on  the  other 
little  or  no  adequate  knowledge  of  the  enormous  number  and  great 
violence  of  submarine  earthquakes,  which  have  recently  been  shown, 
mainly  through  the  important  researches  of  Professor  Milne,  to  be 
the  most  powerful  in  the  deepest  oceans. 

While  volcanoes  and  earthquakes  have  been  associated  from  the 
time  of  Aristotle  and  Pliny,  and  we  think  justly  so,  and  some'mutual 
connection  could  hardly  be  denied ;  yet  even  after  this  relation  was 
especially  affirmed  by  great  original  investigators  like  Humboldt 
and  Charles  Darwin,  it  has  unfortunately  become  customary  of  late 
years  to  class  earthquakes  as  volcanic  and  tectonic  or  structural. 
Instead  of  viewing  volcanoes  as  outlets  of  pent-up-steam,  which 
blows  out  if  possible  the  molten  rock  in  which  it  develops — a  clear 
indication  of  every  great  eruption — an  effort  was  made  to  explain 
earthquakes  as  volcanic,  with  only  partial  success,  whereas  both 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  281 

phenomena  depend  upon  the  common  cause  of  steam  pressure 
formed  deep  in  the  earth's  crust,  principally  by  the  leakage  of  waters 
from  the  sea.  This  highly  explosive  agency  is  developed  so  abun- 
dantly in  the  infinitely  thin  crust  between  the  underlying  molten 
globe,  and  the  overlying  oceans,  the  outcome  of  a  fire  beneath  and 
of  water  above,  as  in  a  boiler,  that  one  should  not  wonder  at  ter- 
rible explosive  or  eruptive  phenomena  appearing  upon  our  planet. 
Considering  the  vast  extent  of  the  oceans  it  would  be  strange  indeed 
if  something  like  volcanoes  and  earthquakes  were  not  inseparably, 
associated  with  the  very  nature  of  the  terrestrial  spheroid. 

If  we  consider  with  attention  the  various  causes  which  might 
be  assigned  to  explain  earthquakes  and  volcanoes,  taking  into  account 
their  recognized  geographical  distribution  and  relation,  the  relative 
situation  of  the  inner  globe  of  fire  and  the  overlying  layer  of  water 
separated  from  it  only  by  the  thin  and  leaky  bottom  of  the  sea,  and 
remembering  that  both  phenomena  are  augmented  to  the  maximum 
in  regions  characterized  by  high  mountains  near  the  deepest  oceans, 
as  on  the  west  coast  of  South  and  Central  America,  the  Aleutian 
and  Kurile  Islands,  Japan,  Sumatra,  Java  and  other  islands  of  the 
East  Indies,  bordering  on  the  deep  waters  of  the  Indian  Ocean,  New 
Zealand,  and  the  Lesser  Antilles  in  the  West  Indies,  Iceland,  Italy, 
Greece,  etc.,  we  shall  find  the  probabilities  that  steam  pressure 
developing  in  the  earth's  crust  is  the  true  and  common  cause  both 
of  earthquakes  and  volcanoes,  are  as  infinity  to  one  against  any  other 
conceivable  cause,  or  all  other  causes  combined.  The  widely  ex- 
tended relationship  here  pointed  out  is  so  intimate  and  everywhere 
so  confirmatory  of  the  theory  that  we  cannot  suppose  it  to  be  due 
to  chance. 

§  3.  Views  of  Professor  Milne  and  his  methods  of  analysis. 

It  has  been  justly  remarked  by  many  seismologists  that  the 
greatest  belt  of  earthquakes  surrounds  the  Pacific  Ocean.  Now  each 
part  of  this  great  "  fire  girdle  of  volcanoes "  with  innumerable 
earthquake  disturbances  has  been  studied  with  care  by  one  or  more 
investigators.  Without  going  into  the  detailed  methods  of  record- 
ing and  charting  developed  by  Professor  Milne,  Professor  Ewing, 
Dr.  Davidson,  Major  De  Montessus  de  Ballore,  Dr.  Agamennone, 
Dr.  Cancani,  Dr.  Vicentini,  Grablowitz,  Omori,  Koto,  Nagaoka,  and 


282  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  ,9, 

others,  which  are  of.  great  value  for  the  close  study  of  particular 
regions,  we  may  call  attention  to  the  conclusions  of  Milne,  and 
Montessus  de  Ballore  regarding  the  slope  of  the  seashores  as  im- 
portant factors  in  the  development  of  earthquakes. 

As  a  result  of  careful  study  of  Japanese  earthquakes  covering 
eight  years,  Professor  Milne  found  that  "the  central  portions  of 
Japan  where  there  are  a  considerable  number  of  active  volcanoes 
are  singularly  free  from  earthquakes.  The  greater  number  of  dis- 
turbances originate  along  the  eastern  coast  of  the  Empire  and  many 
of  them  have  a  submarine  origin."  "  Lines  120  geographical  miles 
in  extent  in  running  in  an  easterly  or  southeasterly  direction  from 
the  highlands  of  Japan  into  the  Pacific  Ocean,  like  similar  lines 
drawn  from  the  Andes  westwards  into  the  same  ocean,  have  a  slope 
of  I  in  20,  or  I  in  30,  and  in  both  of  these  districts  earthquakes  are 
frequent.  On  the  contrary,  along  the  faces  of  flexures  which  are 
comparatively  gentle,  being  less  than  half  of  these  amounts,  which 
may  be  seen  along  the  borders  of  most  of  the  continents  and  islands 
of  the  world,  earthquakes  are  comparatively  rare.  The  inference  is 
that  where  there  is  the  greatest  bending  it  is  there  that  sudden 
yielding  is  most  frequent."1 

It  seems  advisable  to  quote  more  at  length  the  full  line  of  thought 
laid  down  by  Professor  Milne  in  his  classic  work  on  "  Seismology  " 
(London,  1898).  On  page  31  Professor  Milne  says: 

\  "A  very  much  more  serious  objection  to  the  volcanic  origin  of  the 
majority  of  earthquakes  is  the  fact  that  these  disturbances  are  common  in 
the  Himalaya,  Switzerland,  and  other  non-volcanic  regions.  The  destructive 
earthquake  in  1891  in  Mino  and  Owari  occurred  in  a  region  of  metamor- 
phic  and  stratified  rocks.  Again,  an  analysis  of  some  ten  thousand  earth- 
quake observations  of  Japan  shows  that  there  have  been  but  comparatively 
few  which  had  their  origin  near  to  the  volcanoes  in  the  country.  The 
greater  number  of  this  series  originated  beneath  the  ocean  or  along  the 
seaboard,  and  as  they  radiated  inland  they  became  more  and  more  feeble, 
until,  on  reaching  the  backbone  of  the  country,  which  is  drilled  by  numerous 
volcanic  vents,  they  were  almost  imperceptible.  Beyond  this  central  range 
of  mountains,  earthquakes  are  only  rarely  experienced,  and  what  is  true  of 
Japan  seems  to  be  generally  true  for  the  coasts  of  North  and  South  America/'^ 

"  Throughout    the   world    we    find    that    seismic    energy   is    most   marked  • 
along  the  steeper  flexures  in  the  earth's  crust,   in   localities  where  there   is 
evidence  of  secular  movement,  and  in  mountains  which  are  geologically  new 

1  Cf.  Scismological  Journal  of  Japan,  1895,  p.  xv ;  and  Dutton,  "  Earth- 
quakes in  the  Light  of  the  New  Seismology,"  chapter  III. 


I9o5  ]  SEE— THE  CAUSE  OF  EARTHQUAKES.  283 

and  where  we  have  no  reason  for  supposing  that  brady-seismic  movements 
have  yet  ceased. 

"  As  examples  of  the  flexures  to  which  reference  is  here  made,  we  may 
take  sections  running  at  right  angles  to  the  coast  lines  of  the  various  conti- 
nents. The  unit  of  distance  over  which  such  slopes  have  been  measured  is 
taken  at  two  degrees,  or  one  hundred  and  twenty  geographical  miles. 

"The  following  are  a  few  of  such  slopes:' 

West  Coast,   South  America,  near  Aconcagua  i  in  20.2  "1 

The  Kurils  from  Urup  I  in  22.1      Seismic 


in  30.4  |  districts, 
in  23.5 


in 


J 

91     ] 
158 


in  158   I  Non-seismic 

73     r     districts, 
in  243  J 


in 


Japan,  east  coast  of  Nipon 
Sandwich  Islands,  northwards 

Australia   generally 
Scotland  from  Ben  Nevis 
South  Norway 
South  America,  eastwards 

"  The  conclusion  derived  from  this  is  that  if  we  find  slopes  of  consid- 
erable length  extending  downwards  beneath  the  ocean  steeper  than  I  in  35, 
at  such  places  submarine  earthquakes,  and  their  accompanying  landslips 
may  be  expected.  On  the  summit  of  these  slopes,  whether  they  terminate 
in  a  plateau  or  as  a  range  of  mountains,  volcanic  action  is  frequent,  while 
the  earthquakes  originate  on  the  lower  portions  of  the  face  and  base  of 
these  declivities.  Districts  where  earthquakes,  often  followed  by  submarine 
disturbances,  are  most  frequent  are  regions  like  the  northeast  portion  of 
Japan  and  the  South  American  coast  between  Valparaiso  and  Iquique. 
Here  we  have  a  double  folding.  The  sea  bed,  as  it  approaches  the  shore 
line,  instead  of  rising  gradually,  sinks  downward  to  form  a  trough  parallel 
to  the  coast,  after  which  it  rises  to  culminate  in  mountain  ranges.  The 
South  American  trough  which  lies  within  fifty  or  sixty  miles  off  the  coast, 
like  the  Tuscarora  deep  off  Japan,  attains  depths  of  over  four  thousand 
fathoms,  and  the  bottoms  of  these  double  folds  are  well  known  origins  of 
earthquakes  and  sea  wavesjj 

Professor  Milne  then  goes  on  to  show  that  where  secular  move- 
ments are  active,  "  the  forces  which  have  brought  these  mighty  folds 
(mountains)  into  existence  have  not  yet  ceased  to  act."  The  most 
important  question  of  all,  however,  is  what  are  these  forces  ?  He  says 
they  appear  where  "  mountain  formation  is  geologically  of  recent 
origin,"  and  adds  i1 

"The  conclusion  to  which  such  observations  lead  is  that  wherever  we 
find  in  progress  those  secular  movements  which  result  in  the  building  up  of 
countries  or  mountain  ranges,  there  we  should  expect  also  to  find  a  pro- 
nounced seismic  activity.  Thus,  while  admitting  a  few  small  earthquakes 
to  be  volcanic  in  their  origin,  we  recognize  the  majority  of  these  disturb- 
ances as  the  result  of  the  sudden  fracturing  of  the  rocky  crust  under  the 

1 "  Seismology,"  by  John  Milne,  F.R.S.,  p.  33. 


284  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  x9, 

influence  of  bending.  The  after-shocks  which  so  frequently  follow  large 
earthquakes  announce  that  the  disturbed  strata  are  gradually  accommodating 
themselves  to  their  new  position."l 

Professor  Milne's  statement  that  "  the  greater  number  of  this 
series  (10,000  Japanese  earthquakes)  originated  beneath  the  ocean 
or  along  the  seaboard,  and  as  they  radiated  inward  they  became  more 
and  more  feeble,  until,  on  reaching  the  backbone  of  the  country, 
which  is  drilled  by  numerous  volcanic  vents,  they  were  almost 
imperceptible  "  seems  to  point  directly  to  the  cause  set  forth  in  this 
paper.  If  earthquakes  depend  upon  the  explosive  power  of  steam, 
they  ought  not  to  be  numerous  near  the  volcanoes  (unless  these 
vents  get  stopped  up),  but  they  ought  to  be  very  numerous  under 
the  sea  in  the  deep  trough  just  east  of  Japan,  which  he  says  is  found 
to  be  true  by  laborious  and  extensive  observations  covering  a  vast 
number  of  these  phenomena.  In  order  to  leave  no  doubt  as  to  the 
significance  of  these  results  we  shall  consider  also  the  other  lines  of 
thought  which  he  has  worked  out  with  so  much  care. 

§  4.  Inadequacy  of  the  tectonic  theory  based  on  slipping  and 
bending,  and  dislocational  and  fault  movements. 

At  present  we  shall  not  touch  upon  all  the  questions  discussed 
by  Professor  Milne,  but  we  may  remark  that  slopes  of  I  in  20  given 
above  probably  are  not  great  enough  to  produce  the  least  slipping, 
or  fracturing  or  bending  of  rocks.  The  most  effectual  way  to 
convince  ourselves  of  the  truth  of  this  view  is  by  an  appeal  to  the 
cones  of  actual  volcanoes.  Take  Mount  Cotopaxi,  for  example.  It 
is  one  of  the  tallest  active  volcanoes  in  the  world,  and  the  most 
regularly  built  of  all  the  large  volcanoes.  The  slope  is  30°,  the 
angle  of  the  apex  being  120°.  A  slope  of  30°  corresponds  to  I  in 
1.732;  and  thus  Professor  Milne's  ratio  of  I  in  20  is  less  than  one- 
tenth  that  required  to  produce  stability;  and  it  has  escaped  his 
notice  that  slopes  steeper  than  I  in  35  are  not  such  that  the  steepness 
could  give  rise  to  submarine  earthquakes  and  their  accompanying 
landslips.  If  the  cones  of  volcanoes  like  Cotopaxi  do  not  slip,  when 
they  are  more  than  ten  times  steeper  than  the  steepest  sea  slopes, 
and  over  twenty  times  that  mentioned  as  unstable  by  Professor 
Milne,  why  should  slips  occur  under  the  sea?  Obviously  the  steep- 
ness, though  no  doubt  considerable  in  certain  places,  is  not  the  cause 


19o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  285 

of  earthquakes.  Rains,  snows  and  glaciers  on  Mount  Cotopaxi 
ought  to  produce  slipping  of  rocks,  if  anywhere,  because  the  angle 
is  steep  and  the  material  loose  and  unsettled.  We  are  not  aware  that 
the  slipping  of  any  volcanic  cone  or  other  similar  mountain  has  ever 
been  observed  to  produce  a  real  earthquake ;  and  if  slipping  were  the 
order  of  nature,  we  should  expect  some  enormous  slips  with  corre- 
sponding tremors  due  to  this  cause  near  Cotopaxi,  Aconcagua,  and 
other  great  volcanoes  (especially  when  these  mountains  are  shaken 
at  the  times  of  eruption),  which  are  not  observed. 

We  seem  compelled  therefore  to  abandon  the  theory  of  slipping 
and  bending  of  rocks1  except  as  producing  all  the  time  infinitesimal 
tremors  called  microseisms,  which  very  likely  depend  to  a  con- 
siderable extent  on  this  cause.  Glaciers  are  known  to  be  fluid 
masses,  and  they  move  accordingly,  though  very  slowly.  It  has 
been  shown  by  the  writer  (in  Nature,  1902)  that  a  rock  such  as 
marble  undergoes  secular  bending,  and  is  therefore  fluid;  and  we 
take  it  that  all  large  rock  masses  are  very  similar  in  their  behavior, 
though  their  viscosity  may  be  and  generally  is  greater  than  that  of 
marble;  and  hence  if  movement  of  mountain  masses  or  other  large 
rocks  take  place,  it  would  seem  that,  wherever  possible,  it  should 
be  by  a  very  gradual  yielding.  The  cases  in  which  very  large 
masses  of  rock,  like  the  sides  of  a  mountain,  acquire  such  unstable 
positions  as  to  fall,  do  not  seem  to  be  very  numerous.2  Accordingly, 
it  is  difficult  to  believe  that  this  cause  is  very  effective  in  producing 
earthquakes ;  for  such  shocks  as  might  result  from  it  would  be  rare, 
small  and  unimportant.  And  moreover  they  could  never  occur 
where  the  average  slope  is  anything  like  so  small  as  I  in  20.  Be- 
sides the  arguments  here  outlined  there  is  another  hardly  less  effec- 
tive which  we  shall  merely  mention,  namely :  That  the  forces  which 
may  shake  an  entire  continent  and  send  waves  of  compression  and 

1  This  hypothesis  was  originally  proposed  by  Boussingault,  from  observa- 
tions made  on  earthquakes  noticed  in  the  Andes   remote   from  known  vol- 
canoes,  and   has    at   length   developed   into   the   tectonic   theory   now   widely 
held  by  seismologists  and  geologists. 

2  The   movement   by   sliding  of   one   or  two   mountains   in   the   Alps    is 
recorded   within   the   historical   period.     Among   the   Andes   the   most   noted 
change  is  the  collapse  of  the  crater  of  Carihuairazo,  adjacent  to  Chimborazo, 
during  a  violent  earthquake  on   the  night  of   19-20  of  June,    1698.     Before 
this  disaster  Carihuairazo  is  said  to  have  been  taller  than  Chimborazo. 


286  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19 

distortion  through  all  the  rocks  between  the  two  oceans,  and  disturb 
the  whole  earth,  are  not  produced  by  so  small  a  cause  as  the  slipping 
and  bending  of  ledges  of  rock. 

Humboldt  and  Charles  Darwin  long  ago  associated  earthquakes 
with  secular  elevations  and  depressions,  and  it  is  noticeable  that 
Professor  Milne  likewise  thinks  these  disturbances  occur  with  in- 
creased frequency  in  regions  where  such  changes  are  still  in  progress. 

Montessus  de  Ballore  concluded  from  his  elaborate  study  of  sta- 
tistical data  that  in  adjacent  seismic  regions,  instability  of  the  earth 
is  increased  by  differences  of  topographic  relief;  and  that  the 
unstable  regions  are  associated  with  the  greatest  lines  of  corrugation 
of  the  earth's  crust.  Like  Professor  Milne,  he  observes  that  rapidly 
deepening  shores  which  slope  gently,  especially  if  they  are  the  con- 
tinuations of  flat  or  moderately  falling  coast  plains,  are  stable.  His 
results  are  illustrated  by  steep  regions  of  the  seashore  in  South 
America,  Japan,  and  other  parts  of  the  world,  and  by  other  regions 
where  the  slope  into  the  sea  is  more  gradual. 

These  views  and  others  of  similar  tenor  by  several  investigators 
have  led  some  geologists  and  seismologists  to  conclude  that  many 
of  the  earthquakes  noticed  along  shores  which  are  steep  are  due  to 
the  sliding  of  unstable  deposits  of  sediment  settling  on  the  rock 
slopes.  But  if  we  recall,  as  above,  the  smallness  of  these  slopes,  even 
where  the  descent  is  most  rapid — it  never  exceeds  that  of  our 
mountains  upon  the  land,  and  is  seldom  as  steep, — and  observe  that 
the  surrounding  sea  water  is  quiescent  and  would  both  greatly  buoy  up 
and  resist  the  motion  of  any  supposed  sliding  deposit,  so  that  it  is 
doubtful  if  appreciable  sliding  really  takes  place,  and  certain  that 
if  it  does  occur  the  effect  in  disturbing  the  earth  would  be  very 
slight,  we  shall  find  it  difficult  to  believe  that  the  theory  is  well 
founded.  It  appears  that  such  a  deposit,  resisted  by  the  surrounding 
water,  would  slide  with  extreme  slowness,  and  settle  gently  without 
any  appreciable  jar,  and  consequently  no  earthquake  of  importance 
could  be  produced  in  this  way. 


I9o6.|  SEE— THE  CAUSE  OF  EARTHQUAKES.  287 

II.     ON  THE  POROSITY  OF  MATTER  AND  ON  THE  LEAKAGE  OF  THE 

OCEAN  BOTTOMS. 

§  5.  On  the  porosity  and  penetrability  of  matter  under  the  enor- 
mous fluid  pressure  operating  in  the  deepest  oceans,  and  the  under- 
lying crust  of  the  earth. 

Somewhat  extensive  researches  on  the  internal  pressures,  con- 
stitution, and  rigidities  of  the  sun  and  planets,  carried  out  during 
the  past  two  years  and  published  in  the  Astronomische  Nachrichten, 
have  led  the  writer  to  the  conviction  that  many  of  the  laws  of  matter 
depending  on  molecular  forces,  such  as  impenetrability  and  solidity, 
are  quite  inapplicable  to  the  conditions  prevailing  in  the  interior  of 
the  earth  and  other  bodies  of  our  solar  system;  that  under  the 
immense  pressures  there  operating,  whatever  be  the  temperatures, 
but  especially  under  the  high  temperatures  known  to  prevail  in  the 
interior  of  these  masses,  the  hardest  natural  bodies  would  yield 
like  sponges,  and  admit  of  the  most  perfect  interpenetrability  of 
all  the  elements.  The  conclusion  was  reached  from  the  study  of 
forces  of  somewhat  impressive  magnitude  that  all  matter  is  enor- 
mously porous,  and  quite  leaky  under  forces  much  smaller  even  than 
those  operating  in  the  interior  of  the  earth;  so  that  solidity  and 
impenetrability,  long  held  to  be  among  the  most  universal  properties 
of  matter,  far  from  being  absolute,  appeared  to  be  very  relative 
properties,  appropriate  to  very  small,  but  wholly  inappropriate  to 
large,  forces,  and  sometimes  set  aside  by  the  direct  evidence  of  our 
senses  in  common  laboratory  experiments. 

There  doubtless  are  many  experiments  which  would  enable  us  to 
appreciate  the  significance  of  these  general  principles  in  specific 
cases,  but  it  will  suffice  to  recall  one  close  at  hand,  and  directly 
connected  with  the  question  under  discussion.  In  the  series  of 
soundings  of  the  depths  of  the  sea  carried  out  some  years  ago  by 
certain  officers  of  the  United  States  navy  occupied  with  hydrographic 
and  ocean  surveys  it  was  found  that  hollow  glass  balls  with  walls 
several  centimetres  thick,  when  subjected  to  increasing  pressure  at 
various  depths,  came  up  more  and  more  completely  filled  with  water, 
in  proportion  as  the  depth  increased,  though  no  fracture  of  the 
glass  had  occurred,  and  no  holes  in  it  could  be  discovered  by  ex- 
amination of  the  surface  under  the  highest  microscopic  power. 


288  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

After  a  careful  inquiry  by  many  experienced  physicists  the  conclu- 
sion was  reached  that  the  water  had  been  forced  slowly  but  bodily 
through  the  thick  walls  of  the  glass  under  a  pressure  of  less  than 
1,000  atmospheres,  in  an  interval  of  less  than  an  hour's  time. 

In  the  year  1661  a  well-known  'experiment  was  made  by  the 
Florentine  academicians  who  forced  water  through  the  solid  walls 
of  a  sealed  hollow  sphere  of  gold,  and  other  metals,  by  changing  the 
shape  of  the  sphere  under  mechanical  applications  of  pressure,  so 
as  to  diminish  the  volume.  The  present  case  of  the  porosity  of  glass 
was  thus  verified  from  the  opposite  point  of  view,  by  the  steady 
application  of  external  fluid  pressure,  on  the  spherical  surfaces  of 
glass  balls  sent  down  in  modern  soundings  of  the  ocean  depths. 

The  great  porosity  of  all  matter  has  of  course  long  been  recog- 
nized by  physicists,  but  we  are  so  accustomed  to  dealing  with  small 
forces  and  the  resulting  doctrine  of  the  impenetrability  of  matter 
that  it  is  doubtful  whether  our  appreciation  of  this  fact  has  yet 
passed  beyond  the  academic  stage.  In  his  well-known  "  Properties 
of  Matter,"  fourth  edition,  p.  87,  Tait  says : 

"  The  porosity  of  wood,  necessary  for  the  circulation  of  sap,  is  beauti- 
fully shown  by  the  fact  that,  from  microscopic  examination  of  a  thin  slice 
of  fossil  tree,  a  botanist  can  tell  at  once  the  species  to  which  it  belonged. 
The  greater  part  of  the  material  of  the  wood  has  disappeared  for  it  may 
be  millions  of  years,  but  its  microscopic  structure  has  been  preserved  by  the 
infiltration  of  silicious  or  calcareous  materials  which,  hardening  in  the  pores, 
have  thus  preserved  a  perfect  copy  of  the  original.  The  rapid  passage  of 
gases  through  unglazed  pottery,  iron  and  (hot)  steel,  etc.,  shows  the  porosity 
of  these  bodies  in  a  very  remarkable  manner.  So  does  the  strange  absorp- 
tion of  hydrogen  by  a  mass  of  palladium.  The  porosity  of  steel  has  recently 
been  shown  in  a  most  remarkable  manner  by  Amagat,  who  forced  mercury 
through  a  thickness  of  more  than  three  inches  under  a  presure  of  at  least 
four  thousand  atmospheres.  The  metal  was  quite  impervious  to  glycerine 
under  the  same  pressure." 

At  the  time  this  passage  was  written,  some  twenty  years  ago, 
Tait  remarked  that  decisive  proof  of  the  porosity  of  vitreous  bodies, 
such  as  glass,  had  not  yet  been  obtained,  but  added  "  that  they 
form  almost  a  solitary  class  of  exceptions  to  an  otherwise  general 
rule  seems  highly  improbable."  He  then  proceeded  to  show  that  all 
bodies  whatsoever  must  necessarily  be  porous  and  leaky  when  sub- 
jected to  great  fluid  pressure,  and  he  pointed  out  that  the  penetra- 
bility depended  greatly  on  the  character  of  the  fluid,  thus  indicating 
the  great  influence  of  molecular  and  atomic  forces. 


19o6]  SEE— THE  CAUSE  OF  EARTHQUAKES.  289 

To  make  a  practical  application  of  these  principles,  what  shall 
we  now  say  with  respect  to  the  ocean  bottoms?  In  deep  places 
the  pressure  of  the  sea  water  upon  them  is  very  great,  sufficient 
to  force  the  water  through  walls  of  solid  glass  several  centimeters 
thick  in  a  short  time,  and  the  bed  itself  in  general  no  tighter  than 
that  of  a  pond  in  a  common  field.  Obviously,  most  of  these  bot- 
toms will  leak,  and  leak  at  a  rapid  rate  under  the  enormous  pres- 
sure operating  in  the  greatest  depths  of  the  sea.  The  bed  of 
the  ocean  will  not  leak  with  equal  rapidity  in  all  places,  but  almost 
universal  leakage  will  certainly  develop;  and  the  water  will  be 
driven  down  into  the  earth  at  various  rates  depending  upon  the 
fluid  pressure  and  temperature  and  the  physical  character  of  the 
sea  bottom.  Where  the  rock  is  volcanic,  and  badly  fractured,  or 
sandy,  the  leakage  will  be  most  rapid,  and  where  the  bed  is  made  of 
fine  clay  or  unbroken  granite,  the  leakage  will  be  much  more 
gradual.  It  will  also  depend  directly  on  the  depth  of  the  sea,  being  a 
maximum  where  the  ocean  is  deepest,  and  generally  quite  insig- 
nificant in  shallow  water.  The  amount  of  water  leaking  through 
any  square  meter  of  the  sea  bottom  will  be  given  by  an  expression 
of  the  form 

w=P.p.f(t).4>(T), 

where  P  is  the  fluid  pressure  in  the  bed  of  the  sea,  and  thus  directly 
proportional  to  the  depth ;  p  the  average  porosity  of  the  ocean  bot- 
tom, and  thus  depending  on  the  kind  of  ooze,  dust,  sediment  and 
rocks  underlying  the  sea  and  their  state  of  compression;  and  f(t) 
is  some  function  of  the  time,  depending  on  the  average  rate  of 
leakage  through  the  successive  strata;  and  (f>(T)  is  a  function 
of  the  temperature,  and  thus  -increasing  with  the  descent  into  the 
rocks  of  the  earth's  crust.  As  water  is  almost  incompressible  for 
small  or  moderate  forces,  its  escape  downward  would  depend  upon 
the  continued  descent  of  that  which  first  entered  the  bed  of  the 
ocean,  the  rate  of  which  would  be  diminished  under  the  increasing 
pressure  and  density  encountered  in  the  lower  strata,  but  on  the 
other  hand  increased  by  the  rising  temperature  which  makes  the 
rocks  more  penetrable  and  also  augments  their  power  of  absorption. 
Various  values  of  these  quantities,  P,  p,  /(/),  <1>(T),  would  give  the 


290  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

several  rates  of  leakage  for  the  corresponding  areas  of  the  bottom 
of  the  sea.  In  general  it  is  obvious  that  the  leakage  will  be  most 
rapid  where  the  sea  bottom  is  fractured  or  porous,  the  underlying 
temperature  high,  and  the  depth  very  great.  A  rapid  rate  of  leakage 
would  imply  that  large  quantities  of  water  quickly  come  in  contact 
with  the  heated  rock  and  develop  correspondingly  great  steam  pres- 
sure in  the  crust  which  underlies  that  part  of  the  ocean.  Tait's 
remark  about  the  rapid  passage  of  gases  through  hot  steel  ob- 
viously applies  to  the  absorption  and  diffusion  of  steam  in  hot 
rock;  for  this  is  found  by  experiment  to  be  quite  general  for  many 
of  the  metals.  And  in  the  case  of  lava  as  it  pours  from  a  volcano, 
it  is  observed  that  the  molten  rock  emits  vast  quantities  of  vapor, 
of  which,  according  to  Sir  Archibald  Geikie,  999  parts  in  1,000  is 
steam.  This  fact  in  itself  is  extremely  impressive;  for  it  indicates 
that  the  remaining  thousandth  part  of  the  gases  emitted,  including 
vapors  of  sulphur,  hydrogen  sulphide,  hydrochloric  and  carbonic 
acid,  are  derived  from  the  rocks  of  the  earth's  crust  under  the  action 
of  steam  and  the  high  temperature.  We  may  therefore  consider  that 
steam  is  the  only  original  vapor  operating  in  the  crust  of  the  earth. 

§  6.  Daubree's  experiments  on  the  effects  of  capillarity. 

After  this  paper  was  fully  outlined  and  some  references  were 
being  verified,  the  author  had  the  good  fortune  to  notice  the  fol- 
lowing significant  statement  in  Sir  Archibald  Geikie's  admirable 
"  Text  Book  of  Geology,"  fourth  edition,  1903,  p.  354: 

"An  obvious  objection  to  this  explanation  is  the  difficulty  of  conceiving 
that  water  should  descend  at  all  against  the  expansive  force  within.  But 
Daubree's  experiments  have  shown  that,  owing  to  capillarity,  water  may 
permeate  rocks  against  a  high  counter  pressure  of  steam  on  the  further  side, 
and  that  so  long  as  the  water  is  supplied,  whether  by  minute  fissures  or 
through  pores  of  the  rocks,  it  may,  under  pressure  of  its  own  superincumbent 
column,  make  its  way  to  highly  heated  regions.  Experience  in  deep  mines 
rather  goes  to  show  that  the  permeation  of  water  through  the  pores  of  the 
rocks  gets  feebler  as  we  descend." 

In  his  "  Physics  of  the  Earth's  Crust,"  second  edition,  p.  144,  Rev. 
O.  Fisher  also  makes  some  interesting  remarks  on  Daubree's  ex- 
periments, which  are  included  in  his  "  Rapport  sur  les  progres  de 
la  Geologic  experimentale,-"  Paris,  1867.  After  describing  Daubree's 
experiment,  Rev.  Fisher  remarks : 


r9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  291 


M.  Daubree  conceives  that  if  the  layer  of  rock  were  of  great  thickness, 
and  a  very  high  temperature  maintained  in  the  cavity,  a  correspondingly  high 
steam  pressure  would  result,  which  would  be  sufficient  to  raise  lava  in  the 
vent  of  a  volcano,  and  to  produce  earthquakes;  while  the  force  so  obtained 
might  after  expenditure  be  again  and  again  renewed. 

"This  theory  requires  the  occurrence  of  cavities  at  great  depth  (' sup- 
posons  une  cavite  separee  des  eaux  de  la  surface')  communicating  with  the 
volcanic  vents.  But  the  only  argument  in  favor  of  cavities  existing  seems 
to  be  that  the  requisite  mechanical  force  is  obtainable  by  means  of  them; 
but  it  seems  a  priori  impossible  that  there  should  be  such  cavities." 

These  passages  are  of  interest  in  connection  with  Part  VIII. 
of  this  paper,  where  it  is  shown  that  such  cavities  or  partial  cavities 
develop  from  the  expulsion  of  lava  from  under  the  bed  of  the 
sea,  and  the  resulting  subsidence  of  the  bottom  causes  the  great 
sea  waves  which  so  frequently  follow  violent  earthquakes. 

§  7.  Historical  development  of  the  theory  of  the  penetration  of 
sea  water. 

Although  these  passages  were  found  too  late  to  have  influenced 
the  theory  developed  in  this  paper,  they  are  cited  here  for  conveni- 
ence, and  to  show  some  of  the  historical  aspects  of  the  problem  of 
the  penetration  of  sea  water.  It  was  much  discussed  also  in  Hum- 
boldt's  time,  as  we  learn  from  his  remarks  in  the  Cosmos: 

"  The  geographical  distribution  of  the  volcanoes  which  have  been  in  a 
state  of  activity  during  historical  time,  the  great  number  of  insular  and  lit- 
toral volcanic  mountains,  and  the  occasional,  although  ephemeral,  eruptions 
in  the  bottom  of  the  sea,  early  led  to  the  belief  that  volcanic  activity  was 
connected  with  the  neighborhood  of  the  sea,  and  was  dependent  upon  it  for 
its  continuance." 

"For  many  hundred  years,"  says  Justinian,  or  rather  Trogus  Pompeius, 
whom  we  follow,  "  Etna  and  the  Eolian  islands  have  been  burning,  and 
how  could  this  have  continued  so  long,  if  the  fire  had  not  been  fed  by 
the  neighboring  sea?"  In  order  to  explain  the  necessity  of  the  vicinity  of 
the  sea,  recourse  has  been  had  even  in  modern  times,  to  the  hypothesis 
of  the  penetration  of  sea-water  into  the  foci  of  volcanic  agency,  that  is  to 
say,  into  deep-seated  terrestrial  strata.  When  I  collect  together  all  the  facts 
that  may  be  derived  from  my  own  observations  and  the  laborious  researches 
of  others,  it  appears  to  me  that  everything  in  this  involved  investigation 
depends  upon  the  questions  whether  the  great  quantity  of  aqueous  vapours, 
which  are  unquestionably  exhaled  from  volcanoes  even  when  in  a  state  of 
rest,  be  derived  from  sea-water  impregnated  with  salt,  or  rather,  perhaps, 
with  fresh  meteoric  water;  or  whether  the  expansive  vapours  (which  at  a 
depth  of  nearly  94,000  feet  is  equal  to  2,800  atmospheres)  would  be  able  at 


292  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  1 8, 

different  depths  to  counterbalance  the   hydrostatic  pressure  of  the  sea,   and 
thus  afford  them  under  certain  conditions  a  free  access  to  the  focus."  * 

Again  :2 

"  The  great  number  of  volcanoes  on  the  islands  and  on  the  shores  of 
continents  must  have  early  led  to  the  investigation  by  geologists  of  the 
causes  of  this  phenomenon.  I  have  already,  in  another  place  (Cosmos,  Vol. 
I,  p.  242),  mentioned  the  confused  theory  of  Trogus  Pompeius  under  Augus- 
tus, who  supposed  that  the  sea-water  excited  the  volcanic  fire.  Chemical 
and  mechanical  reasons  for  this  supposed  effect  of  the  sea  have  been  adduced 
to  the  latest  times.  The  old  hypothesis  of  the  sea-water  penetrating  into 
the  volcanic  focus  seemed  to  acquire  a  firmer  foundation  at  the  time  of 
the  discovery  of  the  metals  of  the  earth  by  Davy,  but  the  great  discoverer 
himself  soon  abandoned  the  theory  to  which  even  Gay-Lussac  inclined,  in 
spite  of  the  rare  occurrence  or  total  absence  of  hydrogen  gas.  Mechanical, 
or  rather  dynamical  causes,  whether  sought  for  in  the  contraction  of  the 
upper  crust  of  the  earth  and  the  rising  of  continents,  or  in  the  locally  dimin- 
ished thickness  of  the  inflexible  portion  of  the  earth's  crust,  might,  in  my 
opinion,  offer  a  greater  appearance  of  probability.  It  is  not  difficult  to 
imagine  that  at  the  margins  of  the  up-heaving  continents  which  now  form 
the  more  or  less  precipitous  littoral  boundary  visible  over  the  surface  of  the 
sea,  fissures  have  been  produced  by  the  simultaneous  sinking  of  the  adjoin- 
ing bottom  of  the  sea,  through  which  the  communication  with  the  molten 
interior  is  promoted.  On  the  ridge  of  the  elevations,  far  from  that  area  of 
depression  in  the  oceanic  basin,  the  same  occasion  for  the  existence  of  such 
vents  does  not  exist.  Volcanoes  follow  the  present  sea-shores  in  single, 
sometimes  double,  and  sometimes  even  triple  parallel  rows.  These  are  con- 
nected by  short  chains  of  mountains,  raised  on  transverse  fissures,  and  form- 
ing mountain-nodes.  The  range  nearest  to  the  shore  is  frequently  (but  by 
no  means  always)  the  most  active,  while  the  more  distant,  those  more  in 
the  interior  of  the  country,  appear  to  be  extinct  or  approaching  extinction. 
It  is  sometimes  thought  that,  in  a  particular  direction  in  one  and  the  same 
range  of  volcanoes,  an  increase  or  diminution  in  the  frequency  of  the  erup- 
tions may  be  perceived,  but  the  phenomena  of  renewed  activity  after  long 
intervals  of  rest  render  this  perception  very  uncertain." 

§  8.  Views  of  Lucretius  on  the  penetration  of  sea  water  into 
Mtna. 

We  have  quote  the  above  passage  because  of  Humboldt's  saga- 
cious remarks,  some  of  which  deal  with  the  theory  of  the  penetra- 
tion of  sea  water  as  held  by  the  ancients.  He  mentions  Trogus 
Pompeius  under  Augustus  as  the  author  of  the  theory,  but  it  is 
remarkable  that  the  same  views  were  held  by  the  poet  Lucretius 
more  than  half  a  century  before. 

1  Cosmos,  Vol.  I,  p.  242.     Bohn's  translation. 

2  Cosmos,  Vol.  V,  pp.  431-2.     All  the  citations  of  Humboldt's  works  are 
from  the  Bohn  translations. 


i9o6.]  SEE—  THE  CAUSE  OF  EARTHQUAKES.  293 

In  "  De  Rerum  Natura,"  Lib.  VI,  680  et  seq.,  we  read,  accord- 
ing to  Munro's  translation  : 

"  And  now  at  last  I  will  explain  in  what  ways  yon  flame  roused  to  fury 
in  a  moment  blazes  forth  from  the  huge  furnaces  of  ^Etna.  And  first  the 
nature  of  the  whole  mountain  is  hollow  underneath,  underpropped  through- 
out with  caverns  of  basaltic  rocks.  Furthermore,  in  all  caves  are  wind  and 
air;  for  wind  is  produced  when  the  air  has  been  stirred  and  put  in  motion. 
When  this  air  has  been  thoroughly  heated  and  raging  about  has  imparted 
its  heat  to  all  the  rocks  round,  wherever  it  comes  in  contact  with  them, 
and  to  the  earth,  and  has  struck  out  from  them  fire  burning  with  swift 
flames,  it  rises  up  and  then  forces  itself  out  on  high,  straight  through  the 
gorges  ;  and  so  carries  its  heat  far  and  scatters  far  its  ashes  and  rolls  on 
smoke  of  a  thick  pitchy  blackness  and  flings  out  at  the  same  time  stones 
of  prodigious  weight;  leaving  no  doubt  that  this  is  the  stormy  force  of 
air.  Again  the  sea  to  a  great  extent  breaks  its  waves  and  sucks  back  its 
surf  at  the  roots  of  that  mountain.  Caverns  reach  from  this  sea  as  far  as 
the  deep  gorges  of  the  mountain  below.  Through  these  you  must  admit 
(that  air  mixed  up  in  water  passes;  and)  the  nature  of  the  case  compels 
(this  air  to  enter  in  from  that)  open  sea  and  pass  right  within  and  then 
go  out  in  blasts  and  so  lift  up  flame  and  throw  out  stones  and  raise  clouds 
of  sand;  for  on  the  summit  are  craters,  as  they  name  them  in  their  own 
language  ;  what  we  call  gorges  and  mouths." 

In  one  important  part  of  this  passage,  the  text  is  corrupt  and 
the  context,  therefore,  supplied;  yet  there  is  absolutely  no  doubt, 
from  preceding  passages  stating  that  the  sea  penetrates  the  land, 
that  Lucretius  held  that  the  mountain  is  hollow,  the  water  filters 
through  the  crevices  and  cracks  in  the  rocks,  until  it  comes  into  con- 
tact with  the  subterranean  fires  which  convert  it  into  vapors  that 
give  rise  to  the  explosive  violence  witnessed  in  the  eruptions  of 


We  shall  see  hereafter  that  Aristotle  describes  a  volcanic  eruption 
as  due  to  the  urging  blast  of  pent-up  vapor,  but  it  does  not  seem  that 
he  gave  any  satisfactory  explanation  of  how  the  vapor  developed 
within  the  earth's  crust. 

§  9.  Lucretius'  views  on  earthquakes, 

"  Now  mark  and  learn  what  the  law  of  earthquakes  is.  And  first  of 
all  take  for  granted  that  the  earth  below  us  as  well  as  above  is  filled  in 
all  parts  with  windy  caverns  and  bears  within  its  bosom  many  lakes  and 
many  chasms,  cliffs  and  craggy  rocks;  and  you  must  suppose  that  many 
rivers  hidden  beneath  the  crust  of  the  earth  roll  on  with  violence  waves 
and  submerged  stones;  for  the  very  nature  of  the  case  requires  it  to  be 
throughout  like  to  itself.  With  such  things  then  attached  and  placed  below, 
the  earth  quakes  above  from  the  shock  of  great  falling  masses,  when  under- 


294  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

neath  time  has  undermined  vast  caverns;  whole  mountains  indeed  fall  in, 
and  in  an  instant  from  the  mighty  shock  tremblings  spread  themselves  far 
and  wide  from  that  centre.  And  with  good  cause,  since  buildings  beside  a 
road  tremble  throughout  when  shaken  by  a  waggon  of  not  such  very  great 
weight;  and  they  rock  no  less,  where  any  sharp  pebble  on  the  road  jolts 
up  the  iron  tires  of  the  wheels  on  both  sides.  Sometimes,  too,  when  an 
enormous  mass  of  soil  through  age  rolls  down  from  the  land  into  great 
and  extensive  pools  of  water,  the  earth  rocks  and  sways  with  the  undula- 
tion of  the  water  just  as  a  vessel  at  times  cannot  rest,  until  the  liquid 
within  has  ceased  to  sway  about  in  unsteady  undulations.  .  .  . 

"  The  same  great  quaking  likewise  arises  from  this  cause,  when  on  a 
sudden  the  wind  and  some  enormous  force  of  air  gathering  either  from 
without  or  within  the  earth  have  flung  themselves  into  the  hollows  of  the 
earth,  and  there  chafe  at  first  with  much  uproar  among  the  great  caverns 
and  are  carried  on  with  a  whirling  motion,  and  when  their  force  afterwards 
stirred  and  lashed  into  fury  bursts  abroad  and  at  the  same  moment  cleaves 
the  deep  earth  and  opens  up  a  great  yawning  chasm.  This  fell  out  in 
Syrian  Sidon  and  took  place  at  JEg'mm  in  the  Peloponnese,  two  towns 
which  an  outbreak  of  wind  of  this  sort  and!  the  ensuing  earthquake  threw 
down.  And  many  walled  places  besides  fell  down  by  great  commotions  on 
land  and  many  towns  sank  down  engulphed  in  the  sea  together  with  their 
burghers.  And  if  they  do  not  break  out,  still  the  impetuous  fury  of  the 
air  and  the  fierce  violence  of  the  wind  spread  over  the  numerous  passages 
of  the  earth  like  a  shivering-fit  and  thereby  cause  a  trembling"  ("  De  Rerum 
Natura,"  Lib.  VI,  Munro's  translation). 

III.  THE  GEOGRAPHICAL  DISTRIBUTION  OF  VOLCANOES  AND  THEIR 
RELATION  TO  EARTHQUAKE  PHENOMENA. 

§  10.  Four  fundamental  facts  to  be  explained  by  a  theory  of 
volcanoes. 

A  satisfactory  theory  of  the  cause  of  volcanic  action  must  account 
for  the  following  phenomena : 

1.  The  distribution  of  some  400  active  volcanoes  about  the  mar- 
gins of  the  sea,  and  the  numerous  eruptions  which  take  place  in  the 
sea  or  on  islands,  while  none  at  all  occur  inland  at  distances  exceed- 
ing about  100  miles  from  the  ocean  or  equivalent  large  bodies  of 
water. 

2.  The  fact  that  999  in   1,000  parts  of  the  vapors  emitted  by 
volcanoes  is  steam,  as  if  produced  by  the  leakage  of  the  oceans, 
near  which  the  volcanic  vents  always  are  situated. 

3.  Volcanoes  are  particular  mountains,  and  all  mountains  follow 
the  seashore  as  if  formed  in  some  way  by  the  action  of  the  sea  upon 
the  adjacent  land. 


I9o6] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


295 


r  ^VT(  '.'•; 
i-  ?f  r.ff-  <f « 

i       i  *Y  i  >\K 


1'ROC.  AMER.  PHIL.  SOC. ,  XI.V.    184  S,   PRINTED  FEBRUARY   19, 


296  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

4.  The  close  geographical  relationship  existing  between  vol- 
canoes and  earthquakes  throughout  the  world,  and  the  part  played 
by  earthquakes  in  mountain  formation,  and  the  eruption  of  volcanoes. 

These  four  fundamental  facts  seem  to  admit  of  easy  and  natural 
explanation  on  the  hypothesis  that  the  penetration  of  sea  water 
develops  steam  just  under  the  crust  of  the  earth,  and  the  result  is 
the  upheaval  of  mountains  and  the  eruption  of  volcanoes^ 

§  ii.  Professor  Milne's  researches  on  the  distribution  of  earth- 
quakes. 

H)ne  of  the  most  remarkable  results  of  recent  research  is  the 
discovery  of  numerous  regions  greatly  affected  by  submarine  earth- 
quakes, so  that  it  is  now  known  that  these  phenomena  occur  not 
only  on  land,  but  more  especially  under  the  sea.  As  we  shall  treat 
of  this  remarkable  result  hereafter,  we  shall  at  present  confine  our 
attention  to  the  relations  of  earthquakes  and  volcanoes  as  observed 
upon  the  continents.  It  has  long  been  recognized  that  both  groups 
of  phenomena  occur  in  a  series  of  belts,  which  follow  the  same  gen- 
eral regions  of  the  world,  along  certain  so-called  lines  of  weakness 
in  the  earth's  crust.1 

In  a  recent  review  of  earthquakes  published  in  the  British  As- 
sociation Report  for  1902,  Professor  John  Milne  has  outlined  twelve 
principal  seismic  regions,  some  of  them  of  great  extent.  These 
several  belts  include  the  wide  boundaries  of  the  Pacific  Ocean,  the 
Antilles  and  Caribbean  Sea  region,  and  the  great  belt  beginning  at 
the  Azores,  and  extending  through  the  Mediterranean  to  the  Hima- 
layas and  India.  This  last  great  belt  is  the  only  one  in  which  the 
sea  does  not  predominate  over  the  land,  and  even  here,  the  sea  is 
paramount  over  a  large  part  of  the  area  included,  while  the  rest 
includes  or  lies  adjacent  to  the  highest  mountain  range  in  the  world^ 
As  Major  Button  has  remarked,  it  may  be  doubted  whether  all  of  this 
last  region  should  be  included  in  one  area,  except,  perhaps,  as  an 
outline  to  aid  the  memory ;  but  at  all  events,  the  Azores  and  southern 

1  Cf.  Professor  Milne's  work  on  "  Earthquakes,"  edition  1903,  which 
includes  an  excellent  map  of  the  world  giving  the  distribution  of  both  earth- 
quakes and  volcanoes.  As  -earthquakes  in  the  interior  of  the  oceans  until 
recently  were  seldom  recorded,  unless  of  great  violence,  the  earthquakes 
charted  on  the  map  are  chiefly  those  observed  on  the  land,  so  that  the  centres 
of  the  oceans  appear  unduly  vacant. 


I9o6] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


297 


Europe,  made  up  throughout  of  broken  mountainous  regions  ex- 
tending into  the  Mediterranean,  with  the  Black  Sea  and  Caspian  on 
the  east,  are  not  essentially  different  from  the  earthquake  regions 
surrounding  the  Pacific  Ocean. 

In  his  recent  Bakerian  Lecture  at  the  Royal  Society,  March  12, 
1906,  Professor  Milne  explains  his  latest  classification  of  seismic 
regions  as  follows : 

"  Regions  which  lie  on  the  western  suboceanic  frontier  of  the  American 
and  the  eastern  frontier  of  the  Asiatic  continents,  and  regions  which  lie  on 
a  band  passing  from  the  West  Indies  through  the  Mediterranean  to  the 
Himalayas. 

"  In  addition  to  these  there  are  two  minor  regions,  one  following  the 
eastern  suboceanic  frontier  of  the  African  continent,  which  I  have  called 
the  Malagassy  region,  and  an  Antarctic  region  which  lies  to  the  southwest 
of  New  Zealand. 

"  The  following  table  gives  the  number  of  large  earthquakes  or  mass 
displacements  which  have  occurred  in  the  subdivisions  of  these  regions  since 
1899- 


1899 

1900 

1901 

1902 

1903 
ii 

6 

i 
3 

2 

22 

3 
[902, 

ind  s 

1904 

Total. 

Region  of  the  Pacific 
Ocean. 

Western  Atlantic  and 
Eurasian  regions. 

I.   East    Indian    Archi- 
pelago 

ii 
19 
H 

6 

9 
6 

13 

4 
9 
B 
her, 
ance 

17 
5 
ii 

4 

o 

7 
6 

2 

4 
etwee 
1903 
s  wet 

13 
5 
i 

4 

2 

3 
3 

8 

4 
:n  MJ 

,751 
e  rec 

14 

9 
i 

8 

6 
o 

22 

I 

irch, 
arge 
orded 

9 
14 

0 
0 

o 
o 
I 

4 

0 

and 
mall 

75 
59 
3o 
28 

16 

25 
25 

62 

21 

S"ovem- 
disturb- 

2.   The  coast  of  Japan... 
3    Alaskan  coast         .  .. 

4.   Central  America  
5.  West  of  South  Amer- 
ica    

6.   Antillian  region.    ... 

7.  Azores  

8.  Alpine,  Balkan,  Cau- 
casian,    Himalayan 
region  

9.   Malagassy  district  
10.   Antarctic  district  

.Totals... 

Oi 

•56 

4r1 

64.  1    *8 

20 

341 

"  Many  of  the  disturbances  included  in  this  table  are  known  to  have  been 
followed  by  hundreds  and  even  thousands  of  after-shocks.  The  most  active 
district  is  at  present  that  of  the  East  Indies,  which  might  well  be  consid- 
ered as  an  eastern  prolongation  of  the  Himalayan  region.  The  scene  of 
this  activity  it  may  be  noticed,  is  at  the  junction  of  two  lines  of  rock  folding, 
which  meet  almost  at  right  angles.  Whether  the  Antillean  and  Central 
American  region  should  be  separated  is  open  to  question.  If  we  unite  their 
registers  as  belonging  to  two  comparatively  near  and  parallel  earth  ridges, 
the  movements  of  one  influencing  those  'of  the  other,  we  have  a  region  of 
hypogenic  activity  approximate  to  that  of  the  Japan  seas. 


298  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  18, 

"  Generally  it  would  appear  that  these  regions  of  instability  are  to  be 
found  along  the  margins  of  continents  or  tablelands,  which  rise  suddenly 
to  considerable  heights  above  oceanic  or  other  plains. 

"  At  the  present  time  we  may,  therefore,  say  that  megaseismic  disturb- 
ances do  not  occur  anywhere,  but  only  in  districts  with  similar  contours. 
Are  we  dealing  with  primitive  troughs  and  ridges  which  are  simply  altering 
their  dimensions  under  the  continued  influence  of  secular  contraction,  or  do 
these  reliefs  of  seismic  strain  represent  isostatic  adjustments  which  denuda- 
tion and  sedimentation  demand  ?  " 

Professor  Milne  then  discusses  other  possible  causes,  such  as 
the  effects  of  ocean  currents  and  the  seasons,  including  *  meteoro- 
logical causes,  such  as  accumulations  of  ice  and  snow  at  the  poles, 
and  finally  the  motion  of  the  pole  in  the  body  of  the  earth ;  and  he 
says  that  in  about  thirteen  years  between  1892  and  1904,  he  "  finds 
records  for  at  least  750  world-shaking  earthquakes,"  which  affords 
one  an  impressive  idea  of  the  extent  of  his  researches,  and  of  the 
importance  of  the  subject. 

\  In  general  the  "geographical  distribution  of  volcanoes  is  closely 
similar  to  that  of  the  earthquakes,  but  the  latter  are  the  more  general 
and  widely  extended  phenomena,  while  the  former  are  more  special. 
It  is  remarkable  that  the  volcanoes  break  out  in  the  centers  of  the 
earthquake  belts.  This  relation  can  not  be  accidental,  but  points  to 
a  common  cause  underlying  both  phenomena^] 

Besides  the  active  volcanoes  near  the  seashore,  and  on  islands, 
many  of  which  were  heaved  up  originally  by  submarine  eruptions, 
nearly  every  country  has  a  long  list  of  extinct  volcanoes.  The 
islands  in  which  volcanic  eruptions  have  ceased,  may  also  be  viewed 
as  extinct  volcanoes  in  the  sea.  In  this  respect  the  southern  and 
central  Pacific  Ocean  is  particularly  rich  in  extinct  volcanoes,  and 
there  also,  a  great  many  submarine  earthquakes  are  supposed  to 
occur.  But  the  greatest  breeding  ground  for  world-shaking  earth- 
quakes, as  Professor  Milne  says,  are  the  deep  troughs  along  the 
continents,  near  which  many  volcanoes  usually  are  burning.  As 
volcanic  regions,  we  may  mention,  especially,  the  west  coast  of 
South  and  Central  America,  the  Aleutian  and  Kurile  Islands,  Japan, 
the  Philippines,  Sumatra,  Java,  and  adjacent  islands  of  the  East 
Indies,  New  Zealand,  the  region  of  Erebus  and  Terror  in  the 
Antarctic,  and  Iceland,  the  Caribbean  Sea,  with  the  Azores  and 
Canaries,  the  region  of  the  Mediterranean  and  Central  Asia,  west  of 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  299 

the  Himalayas.  In  such  of  these  regions  as  fall  far  within  the  con- 
tinents, the  volcanoes  have  in  all  cases  died  out  for  lack  of  water, 
but  the  earthquakes  still  exist  as  a  survival  of  former  conditions. 
This  is  true,  for  example,  in  the  regions  of  Central  Asia,  which  no 
longer  has  any  active  volcanoes,  though  some  were  active  there  not 
very  long  ago  geologically,  and  thus  exhibit  still  a  fresh  and  even 
sulphurous  appearance. 

§  12.  The  outbreak  of  new  volcanoes  within  the  historical  period. 

It  may  be  mentioned  here  that  within  historical  times  the  follow- 
ing new  volcanoes  have  broken  forth : 

1.  Monte  Nuovo,  eight  miles  from  Naples,.  September  28,  1538. 

2.  Jorullo,  in  Mexico,  September  29,  1759. 

3.  Izalco,   San   Salvador,   February  23,    1770,   5,000   feet  high, 
thrown  up  on  what  was  formerly  a  cattle  farm. 

4.  Las  Pilas,  on  the  Plains  of  Leon,  Nicaragua,  April  n,  1850,  a 
small  volcano. 

5.  Ilopango,    Nicaragua,   January    20,    1880,    a    small   volcano, 
thrown  up  in  a  lake  600  feet  deep. 

6.  Fusiyama,  Japan,  12,365  feet  high,  which  tradition  says  was 
thrown  up  in  a  single  night,  about  300  B.  C. 

7.  Tarewera,  New  Zealand,  January  10,  1886,  a  mountain  with  a 
flat  top,  which  previously  had  given  no  volcanic  indications. 

There  are  perhaps  other  volcanoes,  some  of  them  mentioned  by 
Strabo,  which  have  broken  forth  on  land ;  and  a  good  many  more 
which  have  been  upheaved  in  the  sea. 

Many  old  volcanes  long  extinct  have  burst  forth  into  renewed 
activity,  generally  with  terrible  violence.  Any  volcano  may  become 
extinct  or  dormant,  and  then  again  break  forth.  In  his  work,  on 
"  Volcanoes,"  Professor  Bonney  often  speaks  of  a  mountain  as 
having  lost  its  crater ;  and  mentions  in  this  class  Ixtaccihuatl  and 
Chimborazo ;  but  although  it  is  probable,  it  is  not  certain  that  either 
of  these  has  ever  been  active.1  Yet  according  to  the  view  developed 

1  In  his  two  ascents  of  Chimborazo,  Whymper  found  lava  and  other 
volcanic  indications,  which  had  escaped  the  notice  of  Humboldt  and  Bous- 
singault,  who  did  not  regard  the  mountain  as  volcanic.  The  adjacent  moun- 
tain of  Carihuairazo,  said  to  have  been  higher  than  Chimborazo  before  the 
crater  collapsed,  June  19-20,  1698,  might  have  ejected  the  volcanic  products 
noticed  by  Whymper  on  Chimborazo,  though  it  seems  improbable. 


300  SEE— THE  CAUSE  OF  EARTHQUAKES.  |pctob  r  ,9, 

in  this  paper  any  mountain  may  become  a  volcano,  on  short  notice, 
if  the  internal  violence  is  sufficient  to  break  open  an  outlet  for  the 
vapors  which  always  slumber  beneath.  We  shall  see,  hereafter,  that 
the  mountains  are  all  filled  with  volcanic  materials,  and  an  explosion 
is  all  that  is  required  to  set  them  going,  and  this  is  usually  effected 
by  the  throes  of  an  earthquake.  All  new  volcanoes,  and  old  ones 
when  they  burst  forth  into  renewed  activity,  do  so  with  violent 
earthquake  shocks.  The  shocks  of  an  earthquake  almost  always  have 
some  effect  on  a  burning  volcano,  and  in  earthquakes  remote  from 
erupting  centers,  the  breaking  out  of  a  volcano  causes  the  shocks  to 
cease,  as  was  long  ago  noticed  by  Strabo. 

Since  this  intimate  connection  has  been  observed  again  and 
again,  and  the  volcanic  and  earthquake  belts  are  generally  similar, 
though  not  strictly  identical,  throughout  the  world,  there  is  a  very 
strong  indication  that  both  depend  upon  a  common  cause,  and  that 
cause  is  nothing  else  than  ordinary  steam.  It  is  worth  while  to 
notice  that  as  Central  America  is  a  narrow  country,  with  fairly  deep 
seas  on  both  sides,  it  is  exactly  where  we  should  expect  volcanic 
forces  to  have  great  sway,  and  observation  shows  that  this  is  true 
for  earthquakes  as  wrell  as  volcanoes.  The  recurrence  of  frightful 
earthquakes  in  that  region,  and  the  upheaval  of  three  new  volcanoes 
within  historical  times  speaks  for  itself,  and  shows  that  all  the 
mountains  are  not  yet  finished ;  and  that  some  of  the  land  in  Central 
America  is  being  elevated  by  forces  depending  on  the  influence  of 
the  sea,  whether  volcanic  or  seismic.  As  the  result  of  his  observa- 
tions Darwin  held  that  volcanoes  break  out  in  rising  areas,  most 
likely  because  an  outlet  is  easily  established  when  the  outer  layers 
are  cracked  open  to  a  great  depth. 

§  13.  The  relation  of  earthquakes  to  volcanoes.     . 

In  his  interesting  work  on  "  Earthquakes  in  the  Light  of  the  New 
Seismology,"  p.  43,  Major  Dutton  follows  Professor  Milne  in  his 
classifications,  and  remarks : 

"  Though  it  is  possible  to  indicate  regions  which  present  both  volcanoes 
and  earthquakes,  there  is  no  proof  of  interdependence  between  seismicity 
and  vulcanicity  in  general.  While  there  are  earthquakes  which  are  certainly 
of  volcanic  origin,  the  one  phenomenon  does  not  necessarily  imply  the  other." 

Professor  Milne,  Omori,  Dutton,  and  others  have  recently  at- 
tempted to  disprove  the  relationship  of  earthquakes  and  volcanoes 


i9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  301 


exhibited  by  the  shores  of  the  Pacific  Ocean,  and  their"  mode  of  at- 
tack has  been  to  show  that  the  volcanoes  around  the  Pacific  are  not 
a  continuous  "  girdle  of  fire,"  but  are  bunched  here  and  there,  with 
large  spaces  between;  and  that  while  the  earthquakes  are  also  dis- 
tributed with  some  irregularity,  there  is  no  visible  connection  be- 
tween them  and  the  volcanoes. 

But  if  steam  forming  in  the  earth's  crust  from  sea  water  leaking 
down  is  the  common  cause  of  both  earthquakes  and  volcanoes,  should 
there  really  be  any  immediate  connection  between  the  two  classes 
of  phenomena?  Would  not  volcanoes  develop  chiefly  where  the 
force  of  the  steam  was  sufficiently  powerful  and  suddenly  exerted 
to  break  through  the  crust  or  mountains,  and  therefore  chiefly  in 
the  mountains  along  the  seashore,  where  the  crust  is  greatly  frac- 
tured, and  enables  the  violent  explosions  of  steam  to  blow  open  an 
outlet  by  raising  a  mountain  which  would  burst  into  a  volcano? 
It  is  along  such  shores  also  that  the  leakage  would  be  greatest  and 
most  volcanoes  should  exist,  provided  the  crust  becomes  badly 
fractured. 

If,  on  the  other  hand,  the  crust  is  not  much  broken  and  ex- 
plosions of  steam  cannot  break  through,  would  there  not  result  a 
great  many  earthquakes  of  the  class  now  called  tectonic  because  not 
visibly  connected  with  volcanoes  and  supposed  to  be  due  to  slipping 
of  rocks  or  faults?  When  the  crust  is  wholly  unbroken,  it  would 
naturally  be  very  difficult,  even  for  deep-seated  forces  of  enormous 
magnitude,  to  raise  up  a  mountain  that  would  become  a  volcano, 
because  all  the  overlying  strata  would  have  to  be  violently  broken  in 
such  a  way  as  to  radiate  from  a  point  like  a  star,  and  ordinarily  the 
strain  of  the  imprisoned  steam  is  much  more  easily  released  by  an 
earthquake  which  merely  shakes  up  the  crust  in  such  a  way  that  a 
neighboring  fault  moves  and  the  internal  pressure  is  relieved  and 
equalized  by  scattering,  without  breaking  through  all  the  overlying 
strata  at  one  time. 

This  indeed  appears  to  be  the  process  of  nature,  and  if  we 
consider  it  in  relation  to  volcanoes  and  earthquakes  we  shall  per- 
ceive, in  accordance  with  observation,  that  the  former  should  be  the 
more  special,  the  latter  the  more  general  phenomena.  Also  both 
phenomena  should  occur  under  the  sea,  and  along  the  shores  of  the 


302  SEE-THE  CAUSE  OF  EARTHQUAKES.  [Octob.r  19. 

deepest  oceans ;  but  volcanoes  would  develop  chiefly  in  certain 
regions  where  the  rocks  are  already  broken  in  the  uplift  of  moun- 
tains and  therefore  easily  burst  open,  whereas  earthquakes  might 
occur  in  any  locality  where  the  leakage  of  the  sea  developed  suffi- 
cient steam.  It  is  undeniable  that  this  is  in  accordance  with  obser- 
vation on  our  actual  earth ;  and  it  shows  that  while  both  volcanoes 
and  earthquakes  should  surround  the  Pacific  Ocean,  earthquakes 
are  much  more  widely  and  uniformly  distributed  than  volcanoes. 
Also  in  those  regions  near  actual  volcanoes,  where  the  imprisoned 
steam  has  a  vent,  violent  earthquakes  should  not  occur;  but  if  the 
activity  of  the  volcano  ceases,  the  danger  of  earthquakes  would  be 
increased. 

Humboldt  remarks  that  this  opinion  was  widely  spread  among 
the  people  of  the  Andes,  and  it  would  be  difficult  to  deny  that  this 
result  of  their  long  experience  was  well  founded,  though  confessedly 
they  did  not  know  upon  what  principle  the  dreaded  explosions 
depended. 

If  the  leakage  from  the  sea  has  moderate  uniformity  with  respect 
to  the  time,  it  is  clear  that  the  cessation  of  the  smoke  of  a  volcano 
is  really  one  of  nature's  danger  signals,  since  the  pressure  within 
the  subterranean  reservoirs  of  the  mountain  and  adjacent  regions 
may  then  increase  to  such  a  degree  as  to  become  extremely  dan- 
gerous. Neither  Krakatoa  nor  Pelee  had  been  active  for  long 
periods  before  the  fearful  explosions  of  1883  and  1902.  Krakatoa 
had  been  practically  dormant  for  two  hundred  years,  and  while 
Pelee  had  experienced  an  eruption  in  1851,  it  was  small,  and  no 
Important  explosion  had  occurred  since  I7&2.1  In  the  case  of  Ve- 
suvius the  general  experience  is  the  same — the  longer  the  eruptions 
are  delayed  the  more  violent  they  become.  For  it  appears  that  in 
79  A.  D.  no  eruption  had  occurred  for  about  six  centuries,  and 
Pliny's  description  of  that  outbreak  shows  that  it  was  more  violent 
than  any  that  has  occurred  since.  The  volcano  of  Conseguina  in 
Central  America  illustrates  the  same  principle  by  the  long  repose 
preceding  the  frightful  eruption  of  1835,  which  spread  devastation 
far  and  wide,  and  in  many  ways  resembled  the  terrible  outbreak  of 

1  Cf.  Heilprin,  "  Mont  Pelee  and  the  Tragedy  of  Martinique,"  pp.  61-187, 
188. 


a9o6  ]  SEE— THE  CAUSE  OF  EARTHQUAKES.  303 

Krakatoa.1  It  has  so  often  been  observed  that  the  earthquakes 
ceased  on  the  eruption  of  a  neighboring  volcano,  that  one  cannot 
doubt  that  direct  relief  was  afforded  by  the  eruption. 

Viewing  the  relation  of  earthquakes  and  volcanoes  in  this  light, 
we  can  easily  understand  why  many  of  the  so-called  tectonic  earth- 
quakes are  doubly  severe — much  more  violent  than  those  closely 
connected  with  volcanoes — because  where  no  volcanic  outlet  has 
been  available,  the  explosive  strain  increases  to  an  enormous  extent 
before  it  can  obtain  any  relief  whatever ;  and  when  the  yielding  does 
occur  the  shock  is  one  of  appalling  violence,  and  does  great  damage 
causing  the  slipping  of  rocks,  faults  and  subsidences,  and  is  felt 
over  a  very  large  area,  because  the  explosive  strain  has  become  deep- 
seated  and  intense. 

The  great  depth  at  which  many  of  the  so-called  tectonic  earth- 
quakes have  been  proved  to  occur,  is  at  once  an  argument  against 
the  dislocational  or  faulting  theory,  and  a  convincing  proof  that 
shocks  of  this  type  are  due  to  the  explosive  power  of  superheated 
steam.  These  shocks  are  obviously  too  deep-seated  to  be  accounted 
for  by  subsidences,  and  moreover  the  resulting  vibrations  are  too 
complex  to  be  due  to  mere  slipping  of  a  ledge  of  rock,  as  will  be 
more  fully  explained  hereafter.  It  may  be  shown  that  no  possible 
subsidence  of  rock  faults  could  produce  a  conspicuously  rotatory 
earthquake  like  that  which  destroyed  San  Francisco. 

IV.     THE  GENERAL  CAUSE  OF  THE  FORMATION  OF  MOUNTAINS  AND 
THEIR  GEOGRAPHICAL  DISTRIBUTION. 

§  14.  On  the  formation  of  mountains  and  Cordilleras,  as  illus- 
trated by  the  Andes. 

If  we  consider  the  deep  trough  running  for  a  great  distance 
parallel  to  the  coast  line  of  the  western  shore  of  South  America2 
and  recall  that  other  deep  troughs  of  the  same  kind  exist  parallel 

1  In  chapter  XVI  of  his  valuable  work  on  "  Earthquakes,"  edition  of 
1903,  Professor  .Milne  cites  several  other  eruptions  of  fearful  violence  accom- 
panied in  each  case  by  terrible  earthquakes. 

2  The  trough  is  not  of  uniform  depth  throughout  its  course,  but  the 
depression  is  always  conspicuous,  so  that  everywhere  the  earth's  crust  is 
arched  downward. 


304 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


[October  19, 


to  the  Aleutian  and  Kurile  Islands,  the  east  shore  of  Japan,  the 
west  shore  of  Sumatra  and  Java ;  also  near  New  Zealand  and  vari- 
ous islands  in  the  deepest  oceans,  as  Guam,  the  Bahamas  and  other 
West  Indian  Islands,  we  shall  perceive  that  this  arrangement  is 
not  by  chance.  The  South  American  trough  always  appears  parallel 
to  the  great  mountain  ranges  of  the  Andes,  and  the  fact  that  it  is 

FIG.  3. 


Outline  Map  of  South  America,  showing  the  great  Ocean  Trough  parallel 

to  the  Andes. 

of  about  the  same  volume  as  the  matter  included  in  the  Cordilleras 
appeared  to  be  a  suspicious  circumstance.  The  relation  above  cited 
for  Japan,  Java,  and  other  islands  is  similar,  but  in  the  case  of 
oval  islands  the  adjacent  depression  may  not  be  a  trough,  but  rather 
a  hole  of  somewhat  oval  or  elliptical  figure. 

Some  years  ago  the  writer  noticed  these  remarkable  sinks  while 


I9o6.] 


SEE     THE  CAUSE  OF  EARTHQUAKES.  305 


examining  a  relief  cast  of  the  Atlantic  Ocean  exhibited  in  the  office 
of  the  United  States  Coast  and  Geodetic  Survey  at  Washington,  and 
remarked  that  it  seemed  as  if  the  volumes  of  the  upraised  islands 
were  not  very  much  larger  than  those  of  the  adjacent  depressions. 
Why  should  depressions  exist  so  near  these  elevations  above  the 
sea,  and,  in  the  case  of  mountain  ranges,  so  nearly  parallel  to  them 
for  long  distances?  Is  there  not  obviously  a  direct  connection  be- 
tween the  elevated  land  and  the  unusual  depression  in  the  adjacent 
sea  bottom  ? 

To  understand  just  what  this  connection  is,  we  may  recall  that 
after  the  great  eruption  of  Mt.  Pelee  in  1902,  it  was  found  by  actual 
measurement  that  a  considerable  portion  of  the  adjacent  sea  bottom 

FIG.  4. 


Vertical  Section  perpendicular  to  the  Andes  and  Andean  trough,  drawn  to 
natural  scale,  and  showing  the  mode  of  operation  of  the  trough  in  the 
formation  of  mountain  and  cordilleras. 

had   sunk   down   hundreds   of   fathoms.1      It   is   impossible   to  be- 
lieve that  this  settling  of  the  bottom  of  the  sea  could  be  due  to  the 

1This  statement  is  perhaps  somewhat  too  positive,  for  Dr.  O  .H.  Titt- 
man,  superintendent  of  the  U.  S.  Coast  Survey,  informs  me  that  reliable 
determinations  of  depth  before  the  eruption  of  Pelee  seems  to  have  been 
insufficient  to  decide  the  question  satisfactorily.  The  cables  were  broken, 
and  the  subject  investigated  by  the  French  Commission  (Lacroix,  Alf,  La 
Montagne  Pelee  et  ses  eruptions,  Paris,  1904),  which  includes  M.  Rollet  de 
1'Isle's  investigation  of  the  reported  changes  of  depth  in  the  vicinity  of  Mar- 
tinique. The  French  commission  was  inclined  to  ascribe  the  disturbances  to 
submarine  volcanic  action,  rather  than  to  subsidences.  This,  however,  is  not 
a  matter  of  great  importance ;  for  in  his  work  on  "  Seismology,"  p.  35-36, 
Professor  Milne  mentions  several  well  established  cases  of  subsidences  in 
the  Mediterranean  and  in  the  Pacific  Ocean  off  the  Esmeralda  River  in 
,  Ecuador.  He  points  out  that  "  disturbances  originating  beneath  the  sea, 
which  are  much  more  numerous  than  those  originating  beneath  the  land, 
likewise  emanate  from  a  region  of  strain.  Mr.  W.  G.  Forster,  who  has 
paid  so  much  attention  to  the  earthquakes  of  the  Mediterranean,  tells  us 
that  they  have  been  accompanied  by  great  subsidences  of  the  sea  bottom." 


306  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  i9 

mere  shaking  of  the  earthquakes  accompanying  that  eruption;  and 
we  must,  therefore,  suppose  that  after  matter  had  been  expelled  by  the 
dreadful  explosions  which  destroyed  St.  Pierre  and  devastated  Mar- 
tinique, or  in  earlier  eruptions,  a  subsidence  near  the  roots  of  the 
mountain  actually  took  place.  Again,  in  1835,  Captain  Fitzroy  and 
Charles  Darwin  observed  that  after  the  violent  earthquake  which 
destroyed  Conception,  the  Chilian  coast  line  in  that  region  had 
been  elevated  from  three  to  five  feet  for  several  hundred  miles.  Not 
only  the  coast  but  also  the  whole  country  back  to  the  Andes  was 
raised.  This  could  only  be  explained  by  the  injection  or  forcing  in 
of  a  corresponding  bulk  of  lava  under  the  land ;  and  this  lava  could 
come  from  nowhere  except  from  under  the  bed  of  the  great  trough 
in  the  adjacent  sea.  The  ultimate  effect  would  be  to  cause  the  trough 
of  the  ocean  to  deepen  correspondingly.  And,  moreover,  such  peri- 
odic injections  from  under  the  sea  trough  would  not  only  push  along 
the  ejected  stream  of  lava,  step  by  step,  until  the  end  of  the  column 
reached  the  mountains,  but  the  forces  thus  arising  would  supply 
the  "  lateral  thrusts  "  which  are  said  to  be  much  needed  for  the 
explanation  of  the  upheavals,  the  tipping  of  the  strata,  the  inclina- 
tions and  sometimes  reversed  positions  of  the  rocks,  and  other  geo- 
logical phenomena  observed  in  mountains  like  the  Andes.  Hereto- 
fore the  abundant  phenomena  of  this  kind  noticed  in  all  high  moun- 
tains have  not  been  satisfactorily  explained.  A  correct  theory  must 
account  for  the  inclinations  seen  in  the  mountains  as  well  as  the 
rising  of  the  coast,  and  such  submarine  earthquakes  as  Darwin 
observed  to  precede  the  uplift  of  the  beach  at  Conception.  The 
present  theory  seems  to  be  capable  of  meeting  this  severe  test,  and 
it  requires  us  to  make  no  assumption  except  that  molten  lava  may 
be  forced  from  under  the  bed  of  the  trough,  and  pushed  along  its 
course  beneath  the  crust  by  the  throes  of  successive  earthquakes. 
It  is  recorded  that  a  great  sea  wave  followed  the  Chilian  earth- 
quake of  1835,  and  such  waves  are  very  frequent  along  the  Chilian 
and  Peruvian  coasts.  They  almost  always  follow  an  earthquake,  and 
begin  by  a  recession  of  the  sea  from  the  shore,  which  then  returns 
as  a  great  wave,  carrying  everything  before  it.  Some  have  supposed 
the  sea  bottom  to  subside,  thus  withdrawing  the  water  toward  the 
sink,  till  it  flows  in  on  all  sides  to  fill  up  the  depression,  and  then 


I906.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  307 

piles  up  and  returns  as  a  great  wave  which  continues  to  oscillate 
furiously,  sometimes  for  days  after  the  earthquake.  We  shall  con- 
sider these  waves  more  fully  hereafter,  and  at  present  it  is  sufficient 
to  remark  that  this  explanation  is  satisfactory  for  the  kind  of  waves 
usually  observed  along  the  west  coast  of  South  America. 

We  may  then  suppose  that  in  such  earthquakes  a  very  large 
mass  of  lava  is  forced  from  under  the  sea,  which  then  settles  below 
its  former  level,  and  the  great  wave  follows.  If  the  lava  is  forced 
toward  the  land,  the  coast  or  mountains  are  upraised ;  if  towards  the 
ocean,  a  ridge  may  be  upheaved  there,  or  possibly  a  submarine  vol- 
cano of  large  extent.  In  either  case  the  trough  of  the  sea  bottom 
parallel  to  the  coast  eventually  becomes  less  stable,  and,  at  certain 
intervals,  settles  little  by  little,  when  the  consistency  of  underlying 

FIG.  5. 


lava  has  been  thinned  by  successive  ejections  ;•  and  thus  with  the 
settling  stability  is  again  restored. 

As  the  trough  is  arched  downwards  towards  thfe  exploding  lava 
the  steam  pressure  from  beneath  cannot  force  it  upward ;  and  the 
strain  is  necessarily  relieved  by  motion  of  the  lava  towards  the 
Andes  or  the  ocean — usually  towards  the  mountains  till  the  trough 
gets  broad  and  deep  and  the  mountains  very  far  away  and  so  high 
that  the  movement  of  the  column  offers  unprecedentedly  great  re- 
sistance, when  the  release  will  at  length  become  easier  towards  the 
ocean  by  the  forcing  up  of  ridges  or  volcanoes  along  the  other 
margin  of  the  trough.  Ridges  with  peaks  in  them  will  usually  re- 
sult, and  this  is  the  beginning  of  the  new  Andes  or  Cordilleras,  which 
are  destined  to  rise  slowly  from  the  sea,  leaving  a  deep  valley 
towards  the  ancient  shore,  to  be  drained  and  filled  in  by  erosion. 

Thus    we    explain    some    of   the    remarkable   parallel    ridges    of 


308  SEE- THE  CAUSE  OF  EARTHQUAKES.  [October i9| 

the  Cordilleras.  And  it  is  natural  that  in  this  upheaval  of  the 
crust,  release  of  strain  due  to  subterranean  steam  pressure  should 
occasionally  come  by  the  throwing  up  of  cross  ridges,  sometimes 
enclosing  undrained  areas,  and  thus  lakes  like  Titicaca  are  formed. 
Proceeding  upon  this  simple  and  natural  principle,  we  may  easily 
explain  all  the  chief  characteristics  of  the  Andes.  It  is  impossible 
to  doubt  that  these  mountains  have  been  formed  by  the  very  forces 
which  we  see  still  at  work  there.  The  upheavals  have  been  step  by 
step,  and  earthquakes  forcing  up  the  mountains  have  at  the  same 
time  caused  the  ejection,  by  the  pushing  along  of  a  column  or  rather 
a  layer,  of  the  necessary  matter  from  under  the  sea,  thus  sinking  the 
bottom  into  a  permanent  trough,  while  the  subsidences  accompany- 
ing some  of  the  earthquakes  have  produced  enormous  sea  waves. 
Countless  thousands  and  perhaps  millions  of  these  earthquakes  ancl 
sea  waves  have  occurred  throughout  past  geological  ages. 

The  trough  parallel  to  the  coast  and  the  upheavals  and  sea 
waves  now  observed  are  a  survival  to  show  us  just  how  the  moun- 
tains have  been  formed,  and  where  the  next  mountain  range  will 
form  in  the  sea.  We  can  predict  the  formation  of  the  new  Andes  as 
confidently  as  we  can  an  eclipse,  though  it  will  be  a  much  longer  time 
before  the  new  mountains  develop ;  for  we  recognize  the  cause  to  be 
a  true  one,  and  see  just  how  it  works  by  a  kind  of  self-regulating 
automatic  process.  The  working  of  the  cause  has  been  observed 
near  Mt.  Pelee,  and  the  operation  of  the  same  process  along  the 
South  American  coast  is  proved  by  the  observations  of  Charles  Dar- 
win and  by  the  great  sea  waves  frequently  observed  within  historical 
times. 

§  15.  Investigation  of  the  significance  of  the  observed  lay  of 
mountain  chains  by  means  of  the  theory  of  probability. 

In  their  new  work  on  "  Geology,"  Vol.  I  (p.  543),  Chamberlin 
and  Salisbury  remark  that  the  relationship  between  the  direction  of 
folded  ranges  of  mountains  and  the  adjacent  seacoast  is  "  a  coinci- 
dence that  is  only  in  part  causal.''  There  are,  doubtless,  many  ways 
in  which  this  problem  could  be  treated  by  the  methods  employed  in 
theory  of  probability.  Without  claiming  to  exhaust  the  various  lines 
along  which  the  discussion  might  be  developed,  we  believe  the  fol- 
lowing method  rests  on  equitable  considerations. 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


309 


Imagine  a  mountain  chain  like  the  Andes  which  runs  near  the 
shore  cut  up  into  pieces  each  long  enough  to  reach  the  sea.  If 
there  is  no  physical  cause  why  the  chain  should  be  parallel  to  the 
seashore,  some  of  the  pieces  might  be  expected  to  lie  at  all  angles 
with  respect  to  the  shore  line  of  the  coast  from  o°  to  90°,  and  thus 
the  chain's  most  probable  form  is  that  of  a  zig-zag  line  made  up  of 

FIG.  6. 


short  pieces  lying  at  all  angles.  Take  the  intervals  of  angular  dis- 
tribution of  the  pieces  of  the  chain  at  9°  ;  then,  excluding  the  exis- 
tence of  physical  causes,  any  angle  from  the  first  interval,  o°  to  9°, 
to  the  last  of  these  subdivisions,  81°  to  90°,  must  be  held  to  be 
equally  probable.  At  any  place  there  are  ten  divisions  of  the  quad- 
rant, all  equally  available  for  the  mountain  chain  to  follow.  The 


310  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  ,9, 

probability  that  the  direction  of  a  piece  of  the  chain  will  fall  in  any 
one  of  these  divisions  of  the  right  angle  is  one-tenth ;  and  the  prob- 
ability that  all  the  n  pieces  throughout  the  whole  chain  will  fall  in 
the  same  angular  division  is  (i/io)".  When  n  is  a  large  number,  or 
the  chain  is  long  and  close  to  the  sea,  this  probability  becomes  prac- 
tically zero.  In  such  a  range  as  the  Andes  it  is  observed  that  all  the 
pieces  of  the  chain  do  fall  in  the  first  division  of  the  angle,  between 
o°  and  9°;  and,  hence,  in  general,  the  probability  is  (io)n:  i  that 
the  observed  lay  of  the  chain  so  exactly  parallel  to  the  shore  of  the 
sea  is  not  the  result  of  mere  chance,  but  depends  directly  on  some 
physical  cause  which  has  made  the  chain  essentially  straight  as  well 
as  laid  out  the  general  course  parallel  to  the  sea  coast. 

If  the  chain  had  the  short  bends  in  it  here  assumed  to  be  pos- 
sible, the  total  length  would  be  greater  than  that  of  the  existing 
chain,  and  n  would  be  correspondingly  increased.  The  data  used, 
therefore,  make  n  a  minimum,  and  P  =  i/(io)n  a  maximum  for  the 
given  chain  everywhere  so  closely  following  the  seashore.  Thus 
the  calculated  value  of  P  is  too  large  rather  than  too  small,  with  the 
existing  lay  of  the  chain. 

Another  way  of  reaching  analogous  results  is  to  consider  what 
the  deviation  from  strict  parallelism  is  in  so  long  a  chain,  and  the 
probability  that  the  coincidence  would  be  so  exact  throughout,  when 
all  angles  between  i"  and  324,000"  (the  equivalent  of  90°)  are 
equally  probable.  If  no  physical  cause  is  involved  depending  on 
the  sea,  there  is  no  reason  why  the  chain  should  not  run  at  any  angle 
across  the  shore  line.  Now,  the  Andes  are  made  up  on  the  average 
of  at  least  two  parallel  chains,  and,  the  probability  of  this  double 
parallel  trend  throughout  would  be  only 


324,000       324,000        114,976,000,000 

In  any  case,  we  see  that  for  the  double  chain,  the  chances  are  hun- 
dreds of  billions  to  one  against  strict  parallelism  to  the  seashore. 
In  the  first  method  of  treatment  each  part  of  the  chain  is  con- 
sidered, without  regard  to  the  rest ;  in  the  second  method,  the  chain 
is  viewed  more  as  a  whole,  and  the  individual  parts  neglected.  In 
respect  to  the  first  method,  it  might  be  claimed  that  as  mountains 


19o6.]  SEE—  THE  CAUSE  OF  EARTHQUAKES.  311 

arise  from  foldings  of  the  crust,  and  as  the  earth's  crust  is  thick,  a 
zig-zag  form  with  many  bends  in  it  would  be  improbable,  because  a 
crack  started  in  the  rocks  anywhere  would  be  likely  to  run  in.  a 
straight  line.  There  may  be  some  justice  in  this  criticism,  but  it 
seems  quite  fully  compensated  for  by  the  fact  that  the  chain  actually 
bends  wherever  the  coast  line  alters  it's  course.  Thus  in  practice 
the  chain  is  shown  to  be  capable  of  flexure  wherever  the  shore  line 
changes  its  direction,  and  there  does  not  seem  anything  improbable 
in  many  short  bends,  unless  the  trend  has  some  connection  with  the 
coast.  Whether  the  chain  could  fairly  be  conceived  as  bending  at 
such  short  intervals  is  a  question  we  need  not  enter  into,  for  we  may 
observe  that  short  bends  actually  appear  in  certain  chains,  and  thus 
the  hypothesis  is  not  contrary  to  nature  under  certain  conditions.  In 
the  present  case  we  have  made  no  assumption  as  to  causes,  except 
that  the  lay  of  the  chain  is  independent  of  the  seacoast,  and  hence 
the  hypothesis  postulates  nothing  improbable. 

To  reduce  the  first  method  to  numbers,  we  may  observe  that  the 
length  of  the  chain  of  the  Andes  is  4,400  miles  and  the  average 
distance  from  the  sea  about  66  miles.  Thus 

4,400  i 

n=  ™-  =  66^  or  P=  -—       =  i  :  (decillion)2 


If  other  parallel  ranges  be  included,  this  divisor  would  be  much 
increased,  perhaps  nearly  squared.  On  the  other  hand,  the  method 
of  viewing  the  chain  as  a  whole  makes  the  divisor  a  quantity  of 
the  order  of  one  hundred  billions.  The  truth  must,  I  think,  lie 
somewhere  between  these  extremes.  If  we  were  to  take  account  also 
of  the  mountains  parallel  to  the  Atlantic  coast,  it  would  certainly  be 
moderate  to  conclude  that  the  parallelism  to  the  seashore  noticed 
in  the  whole  of  South  America,  so  far  as  it  depends  on  chance,  would 
be  less  than  i  :  (decillion)2. 

Thus  it  is  clear  that  the  probability  of  a  physical  cause  connect- 
ing the  mountains  with  the  parallel  shore  of  the  sea  is  probably 
more  than  a  decillion  decillions  to  unity,  and  certainly  more  than 
one  hundred  billions  to  unity. 

The  parallelism  noticed  in  North  America  along  the  Pacific  and 
Atlantic  coasts,  is  not  less  pronounced,  nor  is  there  less  extent  of 

PROC.  AMER.   PHIL.  SOC.,  XLV.    184  T,  PRINTED    FEBRUARY  2O,   1907. 


312 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


[October  19, 


mountains  involved.  On  the  contrary,  the  ranges  of  North  America 
exceed  in  length  those  of  South  America.  The  Rocky  Mountains 
are  indeed  farther  from  the  coast  than  the  Andes,  but  the  shore  line 
has  receded  since  they  were  formed;  while  the  Sierra  Nevada  and 
Coast  Ranges  are  nearer  the  present  shore.  When  one  considers 
all  these  circumstances,  including  the  greater  length  of  the  chains, 

FIG.  7. 


and  the  greater  number  of  parallel  ranges,  notwithstanding  their 
distance  from  the  seacoast,  it  will  be  found  that  in  North  America 
P'  is  certainly  not  larger  than  P  as  found  for  South  America. 
Thus  we  may  put  them  approximately  equal  to  each  other,  and  write 

P.  P'=-r-     r  '  7        ^=  l  '  (decillion)4 
(io)66      (io)b6t 

In  Africa  the  mountain  ranges  are  not  high,  but  they  run  quite 


19o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  313 

parallel   to   the   shore.     We   may,   therefore,    without   appreciable 
error  put 


P>=- 


(io)66 

and 

p.  P'.  P"  =  i:  (decillion)6 

In  the  other  three  continents,  Europe,  Asia,  Australia,  the  lay 

FIG.  8. 


of  the  mountains  is  such  as  to  justify  us  in  taking  P'" .  Piv.  Pv  — 
P.  P'.  P".    And,  therefore,  for  the  whole  world,  we  may  safely  take 

P.  Pf.  P".  P'".  Piv.  Pv=i:  (decillion)12 

This  number  is  so  infmitesimally  small,  or  the  divisor  is  so 
fabulously  large,  that  it  becomes  an  absolute  certainty  that  the  paral- 
lelism of  the  mountains  to  the  seashore  depends  on  a  true  physical 
cause,  and  that  cause  can  be  nothing  but  the  action  of  the  sea  itself. 
Since  the  mountains  always  wall  in  the  land,  it  follows  that  they 
are  erected  by  the  sea,  through  injection  of  the  coast  by  lava  ex- 
pelled from  under  the  ocean  bed.  Accordingly,  it  follows  that  the 
crust  is  bent  parallel  to  the  seashore  by  a  true  physical  cause. 


314 


SEE-THE  CAUSE  OF  EARTHQUAKES. 


[October  19, 


If  instead  of  putting  P  =  i  :  (decillion)2  we  had  used  P  = 
i:  (100  billion),  the  final  result  would  have  been  P.  P'.  P" .  P'". 
P*.  PV.  =  I:  (100  billion)6. 

Even  this  divisor  is  so  infinitely  large  that  the  fraction  totally 
disappears,  and  it  becomes  an  absolute  certainty  that  the  lay  of  the 
mountains  depends  on  the  action  of  the  sea  as  a  physical  cause ;  and 
that  action  can  be  nothing  else  than  the  injection  of  the  coast  with 
lava.  By  this  process  the  mountains  were  upheaved.  The  lay  of  the 

FIG.  9. 


mountains  parallel  to  the  sea  is,  therefore,  no  "  coincidence  that  is 
only  in  part  causal,"  but  the  direct  outcome  of  a  general  law  of 
nature.  How  universal  this  law  is  may  be  inferred  from  the  unerr- 
ing precision  with  which  it  is  exemplified  in  a  region  such  as  that 
about  the  Bay  of  San  Francisco.  Here  the  mountains  line  the  shores 
on  all  sides,  and  change  their  course  in  such  a  way  as  to  enclose  the 
bay  with  walls  so  close  by  and  well  fitting  as  to  leave  no  doubt 
about  the  origin  of  the  surrounding  mountains. 

A  deceptive  way  of  viewing  such  an  argument  as  the  foregoing 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


315 


is  to  claim  that  the  sea,  because  of  its  fluid  nature,  flows  into  the 
depressions  in  the  earth's  crust,  which  are  due  to  subsidence  or 
collapse;  and  when  these  depressions  are  filled  up  they  are  bound 
to  be  surrounded  by  higher  regions  of  hills  or  mountains,  due  to 
wrinkles  in  the  crust.  This  method  of  reasoning  ignores  the  exact 

FIG.  10. 


parallelism  to  the  seashore,  which  held  for  every  mountain  chain  in 
the  world  at  the  time  of  its  formation,  and  still  holds  for  nearly  all 
the  principal  ranges,  though  in  a  few  cases  the  lapse  of  ages  has 
modified  the  direction  of  the  shore  of  the  adjacent  sea. 

The  result  here  established  is,  therefore,  a  fundamental  law  of 
nature,  and  it  gives  the  key  to  the  leading  phenomena  of  the  earth's 
surface. 


316  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

§  1 6.  Hozv  a  sea  valley  develops  and  gives  rise  to  parallel  moun- 
tain chains,  as  illustrated  in  the  San  Joaquin,  between  the  Sierra 
Nevada  and  Coast  Range,  in  California. 

We  have  already  seen  that  mountains  are  raised  by  the  injection 
of  the  coast  by  steam-saturated  lava  exploding  beneath  the  earth's 
crust.  To  understand  the  entire  working  of  this  process  under  good 
conditions,  we  might  study  the  different  sea  valleys  now  existing  in 
various  parts  of  the  world,  or  take  one  which  shows  the  characteris- 
tic features  of  the  process.  If  we  could  find  one  in  which  the  process 
is  complete,  but  of  recent  date  geologically,  its  present  form  would, 
no  doubt,  enable  us  to  make  out  the  transformation  which  is  under- 
gone at  different  stages.  The  Sierra  Nevada  mountains,  with  the 
adjacent  San  Joaquin  valley,  appear  to  be  an  ideal  case  to  illustrate 
the  process  in  question. 

A  study  of  the  Sierras  in  California  shows  that  the  western 
slopes  of  these  gigantic  mountains  are  very  gradual — less  than 
one  in  fifty — and  braced  by  many  spurs,  with  deep  intervening 
canons,  of  which  Yosemite  is  the  most  famous.  The  eastern  slopes 
of  the  Sierras  are  about  ten  times  steeper  than  the  western,  and  the 
jutting  spurs  are  largely  wanting.  This  shows  that  the  injecting 
forces  which  raised  these  mountains  came  almost  entirely  from  the 
west ;  and  they  continued  so  long  that  they  finally  gave  the  range  an 
unsymmetrical  form1 — gently  sloping  and  deeply  corrugated  with 
canons  on  the  west,  and  steep  and  precipitous  on  the  east. 

The  form  thus  taken  by  the  Sierras  would  indicate  that  at  a 
late  stage  in  their  history  the  San  Joaquin  valley  took  the  form 
shown  in  the  accompanying  figure,  long  and  sloping  on  the  east  and 

1  The  more  gradual  slope  of  a  mountain  range  toward  the  sea  is  due  to 
two  causes  more  or  less  distinct:  (i)  The  vertical  upheaval  of  the  chain, 
with  the  successive  horizontal  thrusts  which  push  it  little  by  little  from  the 
sea,  thus  naturally  making  the  farther  slope  the  steeper;  (2)  the  subse- 
quent elevation  of  the  shore,  by  injections  under  the  crust,  which  tips  the 
range  still  further  over,  by  raising  the  base  of  an  incline  that  is  already 
gradual.  These  two  causes  combined  will  be  found  to  explain  the  principal 
inequalities  in  the  slopes  of  mountain  ranges  as  observed  in  different  parts 
of  the  world.  When  the  range  is  being  first  upheaved,  the  injections  give 
a  nearly  vertical  uplift;  as  the  range  gets  older  the  injections  come  more 
and  more  from  the  seaward  side;  when  the  range  itself  is  finished,  the 
injections  only  tip  its  base  upward,  and  make  the  seaward  slope  more  and 
more  gradual. 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


317 


steep  and  precipitous  on  the  west.  And  when  this  form  was  once 
attained  the  upheaval  of  the  Coast  Range  became  inevitable.  The 
present  position  of  the  San  Joaquin  river  near  the  western  side  of 
the  valley  still  shows  this  form  of  the  valley,  and  enables  us  to  see 
the  precise  process  of  transformation. 

It  is,  perhaps,  doubtful  whether  the  elevation  of  these  mountains 
has  yet  ceased;  the  earthquakes  in  California  and  the  low  level  of 
the  valleys  would  seem  to  show  that  the  whole  state  is  still  rising, 

FIG.  ii. 


a.     Mountain  formation  just  beginning. 


Mountain  formation  in  the  middle  stages. 


c.     Mountain  formation  in  the  later  stages. 


d.     New  range  rising  from  the  sea. 

and  I  am  told  that  this  is  also  shown  by  beaches  and  shells  at  many 
places  along  the  coast. 

The  same  principles  which  are  here  applied  to  the  Californian 
mountains  can  be  applied  to  other  mountain  ranges  throughout 
the  world. 

§  17.  Significance  of  the  asymmetry  of  a  mountain  chain  with 
respect  to  its  principal  axis. 

It  is  generally  noticed  that  most  mountains  are  unsymmetrical  on 
the  two  sides ;  one  side  has  a  gradual  slope,  while  the  other  is  steep 
and  precipitous.  Moreover,  the  spurs  jutting  out  from  the  range 
are  unequally  divided  between  the  two  sides,  the  larger  number  of 


318  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October*,, 

spurs  being  on  the  side  where  the  slope  is  gradual,-  which  is  always 
turned  toward  the  sea.  Let  us  now  examine  the  meaning  of  this 
arrangement.  In  the  new  work  on  Geology  by  Chamberlin  and 
Salisbury  (Vol.  I,  p.  542-3)  we  read: 

"  Mountain- forming  Movements. — Along  certain  tracts,  usually  near  the 
borders  of  the  continents,  and  at  certain  times,  usually  separated  by  long 
intervals,  the  crust  was  folded  into  gigantic  wrinkles,  and  these  constitute 
the  chief  type  of  mountains,  though  not  the  only  type.  The  characteristic 
force  in  this  folding  was  lateral  thrust.  The  strata  were  not  only  arched, 
but  often  closely  folded,  and  sometimes  intensely  crumpled.  In  extreme 
cases,  like  the  Alps,  the  folds  flared  out  above,  giving  overturn  dips  and 
reverse  strata,  as  illustrated  in  the  chapter  on  "  Structural  Geology,"  pp. 
501-511.  In  these  cases  there  was  an  upward  as  well  as  a  horizontal  move- 
ment, for  the  folds  themselves  were  lifted;  but  the  more  horizontal  thrust 
so  much  preponderated,  and  was  so  much  the  more  remarkable,  that  the 
upward  movement  was  overshadowed.  It  is  well  to  note,  however,  that 
these  mountain  ranges  are  crumpled  outward  and  not  inward,  as  might 
be  expected  if  they  resulted  simply  from  the  shrinkage  of  the  under  side 
of  a  thin  shell.  The  folds  are  sometimes  nearly  upright  and  symmetrical, 
and  sometimes  inclined  and  asymmetrical,  as  illustrated  in  the  chapter  referred 
to.  Where  the  folds  lean,  the  inference  has  been  drawn  that  the  active 
thrust  came  from  the  side  of  the  gentler  slope,  the  folds  being  pushed  over 
toward  the  resisting  side,  and  this  seems  to  be  commonly  true." 

Thus  we  have  good  authority  for  the  statement  that  the  lateral 
thrust  came  from  the  side  of  the  gentler  slope.  It  is  well  known 
that  the  gentler  slope  is  turned  towards  the  sea,  and  thus  we  realize 
that  the  forces  which  pushed  the  mountains  horizontally  was  directed 
from  the  adjacent  ocean. 

In  his  great  work  on  "  Face  of  the  Earth," *  Professor  Suess 
records  the  following  facts,  all  bearing  on  the  above  view : 

1.  In  Vol.  I,  p.  452,  Suess  shows  that  the  tangential  movement 
in  the  Himalayas  and  Burmese  Mountains  on  the  opposite  sides  of 
the  Bramaputra  are  in  opposite  directions,  each  being  directed  from 
the  center  of  the  river — exactly  what  the  present  theory  requires, 
and  not  explainable  on  any  other  hypothesis. 

2.  In  Vol.  II,  p.  34,  Suess  shows  that  the  mountain  folds  in  the 
eastern  part  of  the  United  States  "  have  been  produced  by  a  tan- 
gential movement  directed  from  the  existing  Atlantic  Ocean  toward 
the  mainland."    On  page  139  he  shows  that  the  same  principle  holds 
for  South  America. 

1  Oxford  Translation  by  Dr.  Hertha  Sollas. 


I9o6  |  SEE— THE  CAUSE  OF  EARTHQUAKES.  31i) 

3.  In  Vol.  II,  p.  121,  Suess  shows  that  the  "  prevailing  tangential 
movement  in  the  Alps  and  Pyrenees  "  is  toward  the  north.     Thus 
for  the  Alps,  Lombardy  is  the  most  active  ancient  sea  trough ;  and 
in  the  case  of  the  Pyrenees,  Suess  shows  that  most  of  Spain  was  then 
in  the  bed  of  the  sea,  and  has  since  arisen  (pp.  123-128). 

4.  That  the  Sierra  Nevada  folds  were  produced  by  tangential 
movement  from  the  side  of  the  Pacific  is  generally  recognized  by 
geologists.     Dana  and  others   long  ago  have   remarked  the   same 
thing  about  the  Andes  (Suess,  Vol.  I,  p.  539),  and  recently,  Cham- 
berlin  has  written  me  that  most  of  the  mountains  give  evidence  of 
having  been  upheaved  by  lateral  thrusts  from  the  direction  of  the  sea. 

In  view  of  these  facts  is  not  the  significance  of  the  asymmetry  of 
mountain  chains  perfectly  plain?  The  unsymmetrical  build  of  the 
chains  shows  that  the  forces  by  which  they  were  formed  were  di- 
rected from  the  sea.  And,  as  these  forces  could  not  have  been 
subaerial,  they  must  have  been  subterranean,  working  just  under 
the  earth's  crust,  and  identical  with  those  observed  in  earthquakes, 
when  lava  is  expelled  from  the  sea  and  pushed  under  the  adjacent 
coast,  along  which  the  mountains  always  run  so  exactly  parallel. 

By  no  possibility  could  any  supposed  contraction  of  the  earth 
have  given  rise  to  these  features  in  mountain  structure,  since  in 
that  case  it  would  be  impossible  for  the  shape  of  the  ranges  and 
tilting  of  the  strata,  pointing  to  lateral  thrust,  to  be  always  directed 
from  the  sea.  The  arrangement  and  structure  of  mountains  thus 
contradicts  the  contraction  theory  of  the  globe,  and  shows  that  any 
supposed  effect  of  contraction  was  insensible. 

§  1 8.  Criticism  of  the  contraction  theory  of  the  formation  of  a 
range  such  as  the  Alps. 

In  addition  to  the  considerations  advanced  by  Fisher,  as  ex- 
plained elsewhere  in  this  paper,  to  show  that  mountains  formed  by 
wrinkles  in  the  crust  would  in  no  case  exceed  a  very  small  height, 
and  should,  moreover,  be  distributed  with  some  uniformity  over 
the  globe,  we  may  here  consider  some  objections  to  the  view  that 
a  chain  such  as  the  Alps  has  been  produced  by  shrinkage. 

To  get  Elie  de  Beaumont's  theory  clearly  before  us,  we  quote  it 
as  given  by  Lyell,  "  Principles  of  Geology,"  I2th  ed.,  Vol.  I,  p.  119: 

"  The  origin  of  these  chains  depends  not  on  partial  volcanic  action  or  a 


320  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October*,, 

reiteration  of  ordinary  earthquakes,  but  on  the  secular  refrigeration  of  the 
entire  planet.  For  the  whole  globe,  with  the  exception  of  a  thin  envelope, 
much  thinner  in  proportion  than  the  shell  to  an  egg,  is  a  fused  mass,  kept 
fluid  by  heat,  but  constantly  cooling  and  contracting  its  dimensions.  The 
external  crust  does  not  gradually  collapse  and  accommodate  itself  century 
after  century  to  the  shrunken  nucleus,  subsiding  as  often  as  there  is  a 
slight  failure  of  support,  but  it  is  sustained  throughout  whole  geological 
periods,  so  as  to  become  partially  separated  from  the  nucleus  until  at  last 
it  gives  way  suddenly,  cracking  and  falling  in  along  determinate  lines  of 
fracture.  During  such  a  crisis  the  rocks  are  subjected  to  great  lateral  pres- 
sure, the  unyielding  ones  are  crushed,  and  the  pliant  strata  bent,  and  are 
forced  to  pack  themselves  more  closely  into  a  smaller  space,  having  no 
longer  the  same  room  to  spread  themselves  out  horizontally.  At  the  same 
time,  a  large  portion  of  the  mass  is  squeezed  upwards,  because  it  is  in  the 
upward  direction  only  that  the  excess  in  size  of  the  envelope,  as  compared 
to  the  contracted  nucleus  can  find  relief'  This  excess  produces  one  or  more 
of  those  folds  or  wrinkles  in  the  earth's  crust  which  we  call  mountain-chains." 

It  is  unnecessary  to  dwell  on  the  violence  of  the  hypothesis  that 
the  nucleus  has  shrunk  away  from  the  crust,  as  here  outlined.  So 
far  as  one  can  see,  no  such  result  is  possible,  nor  is  the  shrinkage 
ever  appreciable. 

But  we  may  here  remark  that  a  radial  shrinkage  of  one  mile 
will  give  a  shrinkage  in  the  semi-circumference  amounting  to  3.14 
miles.  Whether  correctly  or  not,  it  has  been  estimated  by  geologists 
that  the  amount  of  folding  in  the  Alps  exceeds  one-third  of  the 
whole  space  now  occupied  by  these  mountains,  the  shortening  of  the 
original  crust  being  placed  by  Heim  at  74  miles.  Analogous  results 
have  been  reached  by  Claypole  and  others  regarding  the  mountain 
ranges  of  America. 

It  should  be  observed  that  to  afford  a  slack  for  folds  amounting 
to  74  miles,  a  radial  shrinkage  of  about  12  miles  is  required,  even 
when  all  of  the  tangential  movement  is  carried  round  to  one  point. 
To  carry  all  the  tangential  movement  round  to  one  point  would 
imply  one  of  two  things :  ( i )  That  the  crust  is  loose  from  the 
globe  it  surrounds,  and  thus  can  be  carried  around  to  one  point 
from  a  whole  semi-circumference,  which  seems  altogether  improb- 
able; (2)  that  if  the  crust  is  thus  shrunk  up  without  being  carried 
around  loose  from  the  globe,  the  matter  underlying  it  must  be 
condensed  to  about  three-halves  its  former  density.  The  cone  of 
matter  underlying  the  Alps,  and  extending  to  the  center  of  the 
earth  would  thus  have  a  density  50  per  cent,  greater  than  that 


i9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  321 


occurring  under  neighboring  areas.  This  latter  result  is  impossible, 
since  observations  show  that  the  matter  under  mountains  not  only 
is  not  denser  than  the  average,  but  actually  lighter  by  an  appreciable 
quantity.  We  know,  therefore,  that  the  wrinkling  has  not  con- 
densed the  matter  underlying  the  mountains. 

On  the  other  hand,  it  seems  equally  incredible  that  the  shrink- 
age of  the  whole  globe  should  be  brought  forward  to  one  point,  as 
if  the  crust  were  loose  from  the  globe  it  covers.  No  part  of  the 
theory  of  mountains  formed  by  wrinkles  of  the  crust  is  to  be  seri- 
ously entertained.  Besides  the  difficulties  just  mentioned,  the 
postulated  radial  shrinkage  of  12  miles  is  too  great.  It  may  well  be 
doubted  whether  a  shrinkage  of  one  mile  in  the  radius  has  taken 
place  since  the  continents  began  to  emerge  from  the  oceans. 

Professor  Suess  (Vol.  II,  p.  552)  says: 

"As  a  result  of  tangential  thrusts,  the  sediment  of  this  (Mediterranean) 
Sea  were  folded  together  and  driven  upwards  as  a  great  mountain  range, 
and  the  Alps  have,  therefore,  been  described  as  a  compressed  sea." 

We  must,  therefore,  seek  the  explanation  of  the  formation  of  the 
Alps  in  some  process  by  which  this  folding  can  have  taken  place  in 
the  sea,  or  along  its  borders,  and  thus  we  reach  the  theory  outlined 
in  this  paper. 

§  19.  Why  ive  abandon  the  contraction  theory  of  mountain  for- 
mation. 

While  the  considerations  here  adduced  for  the  origin  of  moun- 
tains seem  conclusive,  it  may  not  be  wholly  without  interest  to  point 
out  some  difficulties  which  are  not  satisfactorily  met  by  the  con- 
traction theory,  which  is  the  only  one  now  in  general  use.  It  is 
usually  stated  that  mountains  result  from  a  crumpling  of  the 
earth's  crust,  and  that  the  crumpling  takes  place  along  the  principal 
lines  of  weakness.  This  theory  fails  to  explain  the  origin  of  isolated 
peaks  or  associated  groups  of  peaks  which  sometimes  rise  like  cones 
or  groups  of  cones,  often  more  or  less  intersecting,  in  the  midst  of 
comparatively  regular  plains.  A  theory  writh  this  serious  defect  is 
highly  unsatisfactory. 

If  then  the  contraction  theory  fails  to  explain  isolated  peaks  and 
groups,  which  are  sometimes  pushed  up  in  comparatively  level 
plains,  and  fails  to  explain  the  conspicuous  parallelism  to  the  sea- 


322  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19 

shores,  while  the  account  given  of  cross  ranges  and  parallel  ranges 
standing  in  isolation  is  unsatisfactory,  it  must  be  admitted  that  the 
theory  itself  is  not  well  founded. 

The  assumption  that  since  the  continents  began  to  rise  from  the 
oceans  the  earth  has  shrunk  enough  to  produce  great  wrinkles  in 
the  crust  comparable  with  our  high  mountains  is  undeniably  a  violent 
hypothesis.  For  in  the  writer's  paper  on  the  rigidity  of  the  heavenly 
bodies  (A.  N.t  4104),  it  is  shown  that  no  circulation  of  currents 
within  the  earth  has  been  possible  since  the  globe  became  encrusted. 
If  there  are  no  currents  within,  the  propagation  of  heat  outward 
could  take  place  only  by  conduction;  and  from  Fourier's  analytical 
theory  of  heat  we  know  that  the  loss  of  heat  would  be  extremely 
slow,  and  confined  almost  wholly  to  a  shallow  layer  near  the  surface. 
Indeed  it  seems  probable  that  the  shrinkage  of  the  entire  globe  is 
barely  comparable  to  the  secular  contraction  of  the  cooling  crust 
alone.  The  approximate  accuracy  of  this  view  is  confirmed  by  the 
fact  that  the  crust  has  not  cracked  open  by  pulling  apart,  as  it 
would  do  if  the  crust  shrank  much  more  rapidly  than  the  globe  as 
a  whole.  The  fact  that  the  interior  of  the  globe  lost  very  little 
heat,  while  the  crust  cooled  all  the  time,  would  lead  one  to  think  that 
so  far  from  wrinkling  by  contraction,  the  crust  ought  to  have 
cracked  open  by  the  shrinkage  of  the  shell  over  a  nearly  unyielding 
nucleus;  but  no  doubt  the  process  was  too  slow  and  the  rocks  too 
plastic  to  give  rise  to  actual  rupture  of  the  earth's  crust. 

Moreover,  if  the  globe  shrank,  it  is  inconceivable  that  this  shrink- 
age could  fail  to  be  fairly  uniform  in  the  different  equal  areas  of  the 
surface,  and  thus  we  should  expect  the  resulting  wrinkles  to  be 
distributed  over  the  globe  with .  moderate  equality  and  uniformity. 
Instead  of  this,  we  find  the  mountains,  heretofore  assumed  to  be 
wrinkles,  bunched  into  congested  systems,  and  almost  always  paral- 
lel to  the  seashore,  and  larger  in  proportion  to  the  depth  of  the 
adjacent  ocean.  Is  it  therefore  at  all  credible  that  the  mountains 
have  really  been  formed  by  the  shrinkage  of  the  earth  ?  Would  it  be 
going  too  far  to  say  that  the  whole  theory  of  secular  contraction 
as  applied  to  our  encrusted  planet  is  a  misconception  dating  from 
a  time  when  currents  were  supposed  to  circulate  freely  throughout 
a  liquid  globe  ? 


19o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  323 

After  a  careful  consideration  of  the  whole  question,  including 
all  the  forces  at  work,  one  may  well  doubt  whether  the  radius  of  the 
earth -has  shrunk  a  mile  since  the  continents  began  to  emerge  from 
the  oceans.  The  crust  could  easily  accommodate  itself  to  such  a 
small  shrinkage  as  one  part  in  4,000,  without  producing  any  wrink- 
ling whatever. 

This  subject  of  planetary  wrinkles  has  been  treated  mathe- 
matically by  Professor  Sir  G.  H.  Darwin,  in  his  researches  on  the 
"Tides  of  a  Viscous  Spheroid"  (Phil.  Trans.  Roy.  Soc.,  Part  n, 
1879,  P-  588)-  And  while  his  results  are  recognized  to  be  correct, 
on  the  hypothesis,  they  seem  to  me  to  be  inapplicable  to  the  remote 
history  of  the  earth,  because  I  believe  the  shrinkage  to  have  been 
nearly  insensible,  and  certainly  much  less  effective  than  has  been  gen- 
erally supposed. 

In  his  "  Physics  of  the  Earth's  Crust,"  page  118,  Rev.  O.  Fisher 
has  discussed  Darwin's  theory  thus : 

"  It  may  be  replied  to  this  theory,  that  the  formation  of  the  existing 
continents  cannot  be  looked  at  apart  from  their  geological  history,  and  that 
they  are  evidently  dependent  on,  and  as  it  were,  gathered  round,  the  great 
mountain  ranges  in  which  they  culminate.  Although  these  ranges  primarily 
originated  long  ago  in  very  early  geological  times,  their  present  loftiness  is 
due  to  quite  late  movements ;  and,  if  these  had  not  subsequently  occurred, 
they  would  before  now  have  probably  have  been  razed  to  the  sea-level  and 
have  disappeared,  so  that,  whatever  cause  it  was  which  wrinkled  the  conti- 
nents, seems  to  have  continued  active  to  times  comparatively,  if  not  quite, 
recent;  and  the  moon  is  too  far  off  now.  The  occurrence  of  great  changes 
of  level  at  no  very  distant  geological  period  are  manifest  from  such  instances 
as  that  related  by  the  elder  Darwin." 

It  has  always  been  extremely  difficult  to  show  how  contraction 
could  produce  elevation  of  ranges,  and  the  mechanical  explanations 
which  have  been  put  forward  are  admittedly  unsatisfactory.1  The 
spurs  which  so  often  jut  out  from  the  main  ranges  do  not  look  like 
wrinkles  in  the  crust ;  for  they  are  too  numerous  and  terminate  too 
suddenly  at  their  extreme  ends.  The  isolated  parallel  ranges  so 
often  met  with  in  Nevada  and  Southern  California  also  terminate 
too  suddenly  to  be  explained  by  shrinkage,  or  by  lines  of  weakness. 

In  his  work  on  the  "  Physics  of  the  Earth's  Crust,"  second 
edition,  the  Rev.  O.  Fisher  has  discussed  with  much  care  the  inade- 

1  Fisher's  "  Physics  of  the  Earth's  Crust,"  second  edition,  p.  123. 


324  SEE— THE  CAUSE  OF  EARTHQUAKES.  | October  19,. 

quacy  of  the  contraction  theory  to  account  for  the  elevations  of 
mountains  actually  observed  upon  the  earth.  In  the  case  of  a  solid 
globe,  he  finds  (p.  122)  that  the  average  height  of  the  elevations 
would  be  only  six  and  one-third  feet.  By  the  theory  of  probability 
we  easily  see  that  this  would  absolutely  prevent  individual  elevations, 
even  when  exceptionally  favored  by  circumstances,  from  attaining 
any  considerable  height.  In  the  appendix  to  the  second  edition,  page 
58,  he  examines  the  mean  elevations  which  will  result  from  the 
hypothesis  of  a  liquid  substratum,  and  finds  that  when  the  radial 
contraction  is  12  miles,  "the  mean  height  of  all  the  elevations,  due 
to  the  corresponding  corrugation  of  the  matter  above  the  level  owing 
to  secular  cooling,  is  about  44  feet."  "  It  appears,"  he  adds,  "  there- 
fore as  the  result  of  the  investigations  in  this  chapter,  that  the 
hypothesis  of  a  liquid  substratum  does  not  afford  such  an  increased 
amount  of  compression  as  to  render  it  possible  to  attribute  the 
elevation  of  mountains  to  contraction  through  cooling  in  that  case,, 
any  more  than  in  the  case  of  solidity." 

When  one  recalls  that  our  actual  mountains  are  many  hundreds' 
and  even  thousands  of  times  higher  than  the  mean  elevations  re- 
sulting from  the  contraction  theory,  it  is  readily  seen  how  utterly 
devoid  of  foundation  that  theory  really  is.  Considerations  adduced 
in  the  writer's  paper  on  the  rigidity  of  the  heavenly  bodies  show  that 
the  radial  contraction  of  twelve  miles  used  by  the  Rev.  O.  Fisher 
is  probably  at  least  twelve  times  too  large;  so  that  the  highest  ad- 
missible mean  elevations  due  to  shrinkage  would  be  only  a  very 
few  feet. 

It  need  scarcely  be  added  that  the  Rev.  O.  Fisher  must  be 
given  the  chief  credit  for  showing  by  long  and  patient  research 
the  inadequacy  of  this  time-honored  theory,  which  was  originally 
suggested  by  Elie  de  Beaumont  in  1829,  and  was  no  doubt  a  direct 
outgrowth  of  Laplace's  nebular  hypothesis. 

We  thus  seem  compelled  to  abandon  the  contraction  theory  en- 
tirely, and  to  explain  both  peaks  and  ranges  with  their  striking 
parallelism  to  the  coast  by  upheavals  occurring  near  the  sea,  due  to 
the  explosive  power  of  steam,  which  has  heaved  up  the  mountains 
from  beneath.  The  mountains  apparently  show  this  mode  of  forma- 
tion, and  it  explains  with  equal  satisfaction  cordilleras  and  ranges,. 


I9o6.j 


SEE— THE  CAUSE  OF  EARTHQUAKES.  325 


whether  of  continued  or  isolated  character,  with  their  numerous 
jutting  spurs  and  cross  ranges,  and  isolated  peaks,  which  are  well- 
nigh  unintelligible  on  any  other  hypothesis.  And  lastly  it  shows 
that  all  mountains  are  alike  inside,  whether  they  burst  open  and 
become  volcanoes  or  remain  intact. 

A  theory  presenting  so  many  desirable  points  should  have  a 
strong  claim  to  acceptance. 

In  this  connection  one  geological  term  in  extensive  use  might 
perhaps  be  explained.  We  refer  to  the  phrase  Line  of  Weakness  of 
the  earth's  crust,  which  was  employed  by  Leopold  von  Buch  to 
explain  the  arrangement  of  volcanoes  along  the  seashore.  It  .forms 
wherever  the  sea  stands  some  time,  especially  if  the  sea  is  deep, 
because  the  explosive  paroxysms  of  steam  work  under  the  edge  of 
the  sea,  but  not  under  the  land,  and,  therefore,  "  lateral  thrusts  " 
from  the  sea  begin,  while  they  cease  on  the  land;  the  result  is  an 
injection  of  the  coast  line  from  the  direction  of  the  sea,  and  moun- 
tains and  volcanoes  are  upraised,  according  to  the  intensity  and 
especially  the  difference  of  these  forces,  from  the  sea  and  land,  and 
their  duration. 

It  is  not  without  significance  that  the  height  of  the  mountains 
are  in  general  proportional  to  the  depth  of  the  adjacent  sea,  because 
the  forces  of  injection  depend  upon  the  depth,  and  the  elevations 
produced  are  proportional  to  the  intensity  of  these  forces.  When 
the  sea  recedes,  however,  the  extent  of  the  land  gained  is  propor- 
tional to  the  shallowness  of  the  water,  and  hence  arise  the  large  flat 
plains  in  many  countries.  This  explains  the  arrangement  of  moun- 
tains and  volcanoes  along  the  sea  coast,  which  has,  therefore,  been 
called  a  line  of  weakness  in  the  earth's  crust.  As  a  matter  of  fact, 
any  line  will  prove  to  be  weak  where  the  sea  stands  for  a  long  time, 
for  mountains  and  volcanoes  will  be  upheaved  there.  Thus  I  con- 
ceive that  there  is  originally  no  such  thing  as  a  line  of  weakness  in 
the  crust,  and  we  may  with  advantage  dispense  with  that  unfortu- 
nate term.  This  seems  the  more  advisable,  since  the  earth  behaves 
as  a  solid,  and  local  weakness  developed  in  the  formation  of  moun- 
tains has  little  effect  at  a  distance,  except  in  volcanic  regions  or 
ocean  troughs,  which  act  together  sometimes  throughout  their  whole 
extent. 


326  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

It  is  shown  in  the  paper  on  the  rigidity  of  the  heavenly  bodies 
that  the  strength  of  a  planet  like  the  earth  is  not  appreciably  de- 
pendent upon  the  crust,  but  arises  primarily  from  the  great  pressure 
acting  throughout  the  body,  which  itself  in  turn  depends  upon  the 
mass  and  density  of  the  globe.  The  earth's  crust,  therefore,  has 
little  importance  in  the  theory  of  the  eartji,  except  in  our  treatment 
of  surface  phenomena. 

§20.  Is  there  a  creeping  movement  of  the  fluid  substratum  be- 
neath the  crust? 

The  existence  of  such  a  powerful  seismic  zone  around  the 
Pacific  Ocean,  which  is  surrounded  by  unfinished  mountains  and 
a  *  fire  girdle  of  volcanoes '  leads  one  to  inquire  whether  there  may 
not  be  throughout  this  vast  ocean,  as  well  as  in  smaller  seas,  a 
tendency  for  the  explosive  stresses  to  find  relief  at  the  margins, 
by  a  slow  creeping  movement  of  the  particles  of  the  substratum 
towards  the  periphery,  where  the  chief  relief  is  afforded.  For 
those  stresses  arising  under  the  crust  in  the  middle  of  such  an 
ocean,  some  relief  would  be  afforded  by  the  rising  and  sink- 
ing of  certain  oceanic  islands ;  but  a  greater  relief  would  be 
afforded  around  the  periphery  of  the  sea,  where  the  great  moun- 
tain chains  are  in  process  of  formation.  As  the  crust  under  the  sea 
is  incessantly  strained  by  the  heaving  of  subterranean  forces,  some 
parts  rising  and  others  sinking,  a  slow  creeping  movement  of  the 
fluid  substratum  towards  the  periphery  seems  not  only  possible,  but 
perhaps  probable.  Such  a  final  movement  would  be  the  result  of 
the  countless  earthquakes  which  disturb  the  sea  bottom,  and  in  any 
given  earthquake  the  motion  would  be  extremely  slight.  The 
creeping  fluid  would  tend  towards  the  avenues  of  escape  in  islands 
and  on  the  margins  of  the  sea,  as  well  as  towards  areas  still  sub- 
merged but  rising;  and  thus  we  recognize  forces  which  under  cer- 
tain conditions  may  both  elevate  and  depress  islands  in  the  sea ;  but 
in  the  long  run  the  sinking  tendency  will  predominate  where  there 
is  water,  and  the  rising  tendency  where  there  is  land. 

All  along  the  west  coast  of  South  America  Charles  Darwin 
found  conspicuous  evidence  of  elevation  within  recent  geological 
times ;  and  at  Valparaiso  the  amount  was  no  less  than  1 ,300  feet. 
The  periodic  subsidences  indicated  in  certain  places  by  beds  of  ma- 


i9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  327 


rine  fossils  of  past  geological  ages,  could,  I  think,  be  explained  by 
tendencies  developed  under  the  crust,  according  to  which  the  fluid 
substratum  is  alternately  thickened  and  thinned,  owing  to  the  con- 
currence or  non-concurrence  of  the  subterranean  forces.  When 
they  work  towards  a  point  the  result  is  elevation,  and  when  they  tend 
to  diverge  from  a  point  the  result  is  depression,  and  the  elevation 
is  transferred  to  neighboring  areas.  This  is  a  modern  view  of  the 
periodic  movement  of  the  earth's  crust  so  clearly  foreseen  by  Strabo 
nearly  2,000  years  ago. 

According  to  this  view  the  sea  bottoms  may  oscillate,  but  on  the 
whole  tend  to  subside,  not  on  account  of  the  shrinkage  of  the  globe, 
but  by  virtue  of  the  gradual  working  out  of  the  underlying  fluid 
substratum,  which  in  the  long  run  pushes  up  the  land. 

In  his  "  Principles  of  Geology,"  I2th  edition,  Vol.  II,  page  155, 
Lyell  discusses  with  characteristic  fairness  the  historical  cases  of 
elevation  of  coasts  noticed  in  different  parts  of  the  world.  We  shall 
content  ourselves  with  citing  a  very  few  cases  of  this  type :. 

1.  Islands  in  the  sea  innumerable,  both  volcanic  and  non-volcanic 
(apparently,  though  all  are  raised  by  volcanic  forces). 

2.  The  southwestern  end  of  the  Island  of  Crete,  which  even 
Professor   Suess   admits  to   have   experienced   undeniable   secular 
elevation  within  the  historical  period. 

3.  The  region  about  Pozzuoli  and  the  Bay  of  Naples.     This  is 
shown  by  the  famous  temple  of  Jupiter  Serapis,  and  by  the  eleva- 
tion of  the  coast  actually  witnessed  at  the  time  of  the  eruption  of 
Monte  Nuovo  in  1538.     This  raising  of  the  land  was  confirmed  on 
a  larger  scale  for  the  whole  Bay  of  Naples  during  the  Vesuvian 
eruption  of  April,  1906   (cf.  Quarterly  Journal  of  the  Geological 
Society,  No.  247,  1906),  by  Professor  Lorenzo,  who  found  the  ele- 
vation of  the  land  at  Pozzuoli  to  be  six  inches,  and  at  Portici  one 
foot. 

4.  The  foundations  of  both  ^Etna  and  Vesuvius  were  laid  in 
the  sea. 

5.  Professor   Suess   cites   the   most   ample   evidence   of   raised 
beaches  and  other  sea  marks  high  above  the  present  strand  in  almost 
all  parts  of  the  world.    As  these  heights  are  very  unequal,  they  can- 
not be  explained  by  a  simple  sinking  of  the  sea  level,  but  there  must 

PROC.  AMER.  PHIL.  SOC.,  XLV.  184  U,  PRINTED  FEBRUARY  2O,  1907. 


328  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

have  been  undeniable  oscillations  of  the  land,  similar  to,  but  on  a 
larger  scale,  than  those  observed  during  the  historical  period. 

6.  Conclusive  proofs  of  the  upheavals  of  the  Chilian  coast  during 
the  earthquakes  of  1822,  1835,  etc.,  have  been  given  by  Lyell,  and 
will  not  be  repeated  here.  We  content  ourselves,  therefore,  with  the 
following  account  of  the  Valparaiso  earthquake  of  August  16,  1906, 
which  speaks  for  itself: 

THE  GREAT  EARTHQUAKE  AT  VALPARAISO,  AUGUST  16,  1906. 

A  special  copyrighted  cablegram  to  the  San  Francisco  Examiner  of 
August  23,  dated  Valparaiso,  Chili,  August  22,  says : 

"  The  recent  seismic  disturbances  in  this  region  have  thrown  up  several 
new  islands  in  Valparaiso  Bay.  These  islands  are  of  various  dimensions, 
some  being  very  extensive  while  others  appear  to  be  mere  cone-like  rocks 
jutting  above  the  waters.  It  is  reported  that  islands  have  appeared  at  dif- 
ferent points  along  the  coast  of  Chili.  .  .  . 

"  The  wrenching  given  the  earth's  surface  is  still  showing  more  and  more 
day  by  day.  In  sections  of  the  harbor  and  on  the  coast,  the  shore  line  has 
been  materially  changed.  Promontories  have  slid  bodily  into  the  sea  and 
in  other  places  strips  of  coast  line  have  been  completely  submerged.  The 
theory  is  that  there  has  been  a  great  uplift  of  the  Andes  so  as  to  change 
almost  entirely  the  contour  of  the  hilly  region  of  the  republic.  Landslides 
are  everywhere  in  evidence.  Mountain  sides  have  been  stripped  away  and 
chasms  in  the  hills  filled  up. 

"  Persons  who  have  arrived  here  on  horseback  from  points  along  the 
coast  say  that  they  witnessed  nothing  but  devastation.  Whole  villages  were 
wiped  out."  * 

1  Since  this  paper  was  finished,  Professor  H.  D.  Curtis,  in  charge  of  the 
D.  O.  Mills  Expedition  of  the  Lick  Observatory,  at  Santiago,  Chili,  has 
written  an  interesting  letter  to  Professor  Kroeck  of  the  Pacific  University  at 
San  Jose,  which  is  published  in  the  San  Francisco  Argonaut  of  November  3. 
Professor  Curtis  says: 

"  A  Commission  has  been  appointed  to  study  the  shock  and  its  causes.  I 
published  a  statement  that  the  primary  cause  was  doubtless  the  same  as  at 
San  Francisco,  the  slipping  or  sliding  of  one  stratum  past  another,  due  to 
the  well-known  geological  fact  that  the  Coast  of  Chili  is  very  slowly  rising. 
I  learn  since  that  the  Bay  of  Valparaiso  is  now  ten  feet  shallower.  So  I 
think  the  displacement  in  this  shock  will  prove  to  be  mainly  vertical.  It 
may  be  that  the  centre  of  disturbance  was  under  the  sea,  as  Valparaiso  suf- 
fered much  more  than  Santiago." 

Professor  George  Davidson,  President  of  the  Seismological  Society  of 
America,  informs  me  that  during  the  great  earthquake  at  Yakutat  Bay,  near 
Mt.  St.  Elias,  Alaska,  September  3-20,  1899,  the  land  at  the  head  of  Yakutat 
Bay  was  raised  47%  feet.  In  the  Bulletin  of  the  Geological  Society  of 
America,  vol.  17,  May,  1906,  will  be  found  a  careful  investigation  by  Tarr 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  329 

§21.  Avicenna's  views  on  mountain  formation. 

Lyell  .justly  remarks  that  it  is  surprising  to  find  among  the 
extant  fragments  of  Avicenna,  Arabian  physician  and  astronomer 
of  the  tenth  century,  a  treatise  on  the  "  Formation  and  Classification 
of  Minerals,"  characterized  by  considerable  merit,  the  second  chap- 
ter of  which  is  "  On  the  Cause  of  Mountains."  Mountains,  accord- 
ing to  Avicenna,  are  formed,  some  by  essential,  others  by  accidental 
causes.  And  in  illustration  of  the  essential  causes,  he  cites  "  a 
violent  earthquake,  by  which  land  is  elevated,  and  becomes  a  moun- 
tain." In  regard  to  the  accidental  causes  he  mentions  excavation 
by  water  or  erosion,  which  produces  cavities,  such  that  adjoining 
land  is  made  to  stand  out  and  form  eminences. 

The  theory  of  mountain  formation  adopted  in  this  paper  was 
therefore  foreshadowed  by  Avicenna  in  the  tenth  century  of  our  era. 
It  is  extremely  remarkable  that  so  simple  an  explanation  should 
have  been  allowed  to  slumber  for  so  many  centuries,  while  artificial 
and  highly  unsatisfactory  hypotheses  were  in  use. 

V.  EXPLANATION  OF  THE  ELEVATION  OF  PARTICULAR  MOUNTAIN 
RANGES  AND  PLATEAUS. 

§  22.  On  the  uplifting  of  the  Andes. 

We  have  already  seen  that  the  Andes  have  been  uplifted  by  the 
injection  of  lava  beneath  the  crust  in  the  earthquakes  incident  to 
the  heaving  of  the  Andean  Valley  in  the  adjacent  sea.  This  has 
been  the  chief  cause  of  the  original  uplift  of  these  great  mountains, 
and  the  resulting  explanation  suffices  to  account  for  all  the  principal 
phenomena.  Thus  we  explain  the  gentle  slope  of  the  mountains 

and  Martin,  who  show  that  the  coast  was  elevated  for  more  than  a  hundred 
miles,  though  slight  depressions  also  occurred  in  a  few  places.  Elevations  of  7 
to  20  feet  were  common,  and  so  little  change  had  occurred  in  1905  that  Tarr 
and  Martin  were  able  to  illustrate  their  memoir  by  photographs  of  the  most 
convincing  character.  The  barnacles  and  other  marine  animals  were  still 
adhering  to  the  rocks,  and  there  could  be  no  possible  doubt  about  the  fact 
of  the  elevation.  The  depression  of  some  areas  was  made  equally  clear  by 
the  encroachment  of  the  salt  water  upon  forests,  which  were  thus  killed.  Two 
of  the  shocks  at  this  great  earthquake  (September  10-15)  were  particularly 
terrible,  the  motions  recorded  in  Tokio,  3,300  miles  away,  being  ^  and  y% 
inch  respectively.  Note  added  December  3,  1906. 


330  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October^, 

on  the  west  and  the  extreme  steepness  of  the  descent  on  the  east;1 
and  we  also  account  for  the  more  numerous  jutting  spurs  on  the 
west.  On  the  whole  side  spurs  are  much  less  conspicuous  on  the 
east,  where  descent  is  more  rapid.  These  characteristics  are  prob- 
ably the  leading  features  of  the  Andes,  but  there  are  others  deserv- 
ing of  attention,  among  which  we  may  mention  the  following : 

1.  Very  great  volcanic   violence  throughout  the   whole   range, 
and  in  the  peaks  of  the  eastern  as  well  as  of  the  western  cordillera. 

2.  Enormous  vertical  uplifts,  or  fault  movements,  often  amount- 
ing to  thousands  of  feet,  occurring  throughout  the  cordillera,  but  be- 
coming especially  predominant  on  the  eastern  side. 

3.  The  vertical  uplifting  of  enormous  plateaus  such  as  those  of 
Quito,  Caxamarca,  Cuzco  and  Titicaca,  the  latter  being  12,500  feet 
above  the  sea. 

The  heaving  of  the  Andean  Valley  in  the  sea  seems  to  be  the 
principal  cause  of  the  original  elevation  of  the  mountains,  but  it 
appears  probable  that  after  the  mountains  were  raised  to  great 
height  another  secondary  cause  contributed  to  the  forces  operative 
in  producing  the  present  enormous  elevation.  This  secondary  force 
was  nothing  else  than  the  soaking  tropical  rains  constantly  drench- 
ing the  eastern  slope  of  the  mountains.  As  the  earth's  crust  was 
already  broken  and  faulted,  the  leakage  of  the  water  downward 
would  be  facilitated,  while  the  ceaseless  character  of  the  rainfall 
would  make  the  eastern  slope  of  the  Andes  to  all  essential  purposes 
an  inland  sea.  Effectively,  therefore,  this  great  range  of  mountains 
is  built  upon  a  narrow  strip  of  land  with  seas  on  both  sides  like  the 
mountains  in  Central  America,  and  hence,  the  violence  of  th*e  vol- 
canoes and  earthquakes  becomes  more  easily  intelligible. 

To  make  this  theory  more  specific  we  may  recall  that  all  the 
principal  peaks  about  Quito  have  been  volcanic,  and  three  or  four 
volcanoes  are  still  terribly  active  there  now.  Just  east  of  Quito,  at 
the  head  of  the  Amazon  Valley,  are  the  most  terrible  rainfalls  on 

1  Professor  Solon  I.  Bailey,  of  Harvard  Observatory,  who  crossed  the 
Andes  twice,  once  near  Sorata,  Bolivia,  and  again  at  the  Aricoma  Pass,  and 
traversed  the  eastern  ran<ye  a  third  time  through  the  river  Urubamba,  writes 
me  that  his  impression  is  that  the  eastern  slope  is  two  or  three  times  steeper 
than  the  western  slope.  Few  observers  have  had  better  opportunities  of 
judging  of  the  general  structure  of  the  Central  r\ndes  than  Professor  Bailey. 


I9o6.]  SEE— THE  CAUSE  OF   EARTHQUAKES.  331 

the  earth ;  and  this  region  is  so  near  to  Cotopaxi,  Sangay  and  other 
active  vents  as  to  leave  little  doubt  that  it  contributes  to  the  activity 
of  the  volcanoes.  In  Whymper's  account  of  his  "  Travels  among 
the  Great  Andes  of  the  Equator,"  p.  240,  he  cites  an  interesting  pas- 
sage from  the  "  Royal  Commentaries  of  Peru,"  p.  632,  which  runs 
thus : 

"  By  reason  of  the  continual  Rains,  and  moisture  of  the  Earth,  their 
woolen  Clothes  and  linen  being  always  wet,  became  rotten,  and  dropped  from 
their  Bodies,  so  that  from  the  highest  to  the  lowest  every  Man  was  naked, 
and  had  no  other  covering  than  some  few  Leaves.  ...  So  great,  and  so 
insupportable  were  the  Miseries  which  Gonzalo  Pigarro  and  his  Companions 
endured  for  want  of  Food,  that  the  four  thousand  Indians  which  attended 
him  in  this  Discovery,  perished  with  Famine.  .  .  .  Likewise  of  the  three 
hundred  and  forty  Spaniards  which  entred  on  this  Discovery,  two  hun- 
dred and  ten  dyed,  besides  the  fifty  which  were  carried  away  by  Orellana. 
.  .  .  Their  Swords  they  carried  without  Scabbards,  all  covered  with  rust, 
and  they  walked  barefoot,  and  their  Visages  were  become  so  black,  dry  and 
withered,  that  they  scarce  knew  one  the  other;  in  which  condition  they  came 
at  length  to  the  Frontiers  of  Quitu,  where  they  kissed  the  Ground,  and  re- 
turned Thanks  to  Almighty  God,  who  had  delivered  them  out  of  so  many 
and  so  imminent  dangers." 

In  his  account  of  the  ascent  of  Sara-urcu,  Whymper  says 
(p.  241): 

.  .  .  The  scouts  came  back  with  -bad  reports.  The  animals,  they  said, 
could  go  no  farther;  there  was  an  end  to  paths  and  trails,  except  occasional 
wild-beast  tracks ;  there  was  nothing  whatever  to  eat,  and  everything  must 
be  carried;  there  was  no  place  to  camp  upon,  the  whole  country  was  a 
dismal  swamp ;  and  everlasting  rain  was  falling ;  so  much  so  that,  although 
they  supposed  they  had  been  near  to  Sara-urcu,  they  were  quite  unable  to  be 
sure.  ..." 

Pages  241—242 : 

".  .  .  This  (food)  arrived  late,  and  delayed  us  so  much  that  we  could 
not  reach  the  next  camping-place  by  nightfall,  and  had  to  stop  in  a  swamp, 
on  a  spot  where,  if  you  stood  still,  you  sank  up  to  the  knees  in  slime.  This 
place  was  just  on  the  divide,  nearly  13,000  feet  above  the  sea,  and  during  the 
greater  part  of  the  eleven  hours'  night  sleet  or  rain  fell,  rendering  it  well-nigh 
impossible  to  keep  up  a  fire  out  of  the  sodden  materials.  For  me  the  men 
constructed  a  sort  of  floating  bed,  cutting  down  reeds,  and  crossing  and 
recrossing  them,  piling  them  up  until  they  no  longer  sank  in  the  slime.  For 
themselves  they  made  smaller  platforms  of  a  similar  description,  and  sat  on 
their  heels  during  the  whole  night,  trying  to  keep  up  a  fire.  ..." 

Page  242 : 

"...  The  land  was  entirely  marshy,  even  where  the  slopes  were  con- 
siderable; and  upon  it  there  was  growing  a  reedy  grass  to  the  height  of 


332  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

eight  to  ten  feet,  in  such  dense  mass  as  to  be  nearly  impenetrable.  The 
machetas  were  found  inadequate.  It  would  have  taken  several  weeks'  labour 
of  our  whole  party  to  have  cleared  a  track  over  a  single  mile.  The  only 
way  of  getting  through  was  by  continually  parting  the  reeds  with  the  hands 
(as  if  swimming),  and  as  they  were  exceedingly  stiff,  they  sprang  back 
directly  we  let  go,  and  shut  us  out  of  each  other's  sight.  The  edges  of  the 
leaves  cut  like  razors,  and  in  a  short  time  our  hands  were  streaming  with 
blood,  for  we  were  compelled  to  grasp  the  stems  to  prevent  ourselves  from 
sinking  into  the  boggy  soil.  On  this  day  we  crossed  the  divide,  and  the 
streams  now  flowed  toward  the  Atlantic.  The  whole  country  was  like  a  satu- 
rated sponge.  ..." 

Page  243 : 

"...  everything  burnable  was  dripping  with  moisture,  and  the  sur- 
rounding land  was  so  wet  that  water  oozed  or  even  squirted  out  in  jets  when 
it  was  trodden  upon.  ..." 

Page  245 : 

"...  Rain  continued  without  intermission.  No  one  at  Cayambe  had 
spoken  about  these  incessant  rains.  From  the  aspect  of  the  country  (so 
different  from  any  other  part  of  Ecuador),  from  the  saturation  of  the  hills, 
the  innumerable  small  pools,  streamlets  and  springs,  I  am  convinced  they 
.are  nearly  perpetual.  ..." 

In  an  excellent  account  of  "  A  New  Peruvian  Route  to  the  Plain 
of  the  Amazon,"  published  in  the  National  Geographic  Magazine 
for  August,  1906,  Professor  Solon  I.  Bailey,  of  Harvard  College 
Observatory,  describes  the  route  through  the  Aricoma  Pass  at  an 
altitude  of  16,500  feet,  and  continues  (p.  439)  : 

" .  .  .  On  reaching  the  eastern  crest  of  these  mountains,  if  the  view 
is  clear,  one  seems  to  be  standing  on  the  edge  of  the  world.  The  eye,  in- 
deed, can  reach  but  little  of  the  vast  panorama,  but  just  at  one's  feet  the 
earth  drops  away  into  apparently  endless  and  almost  bottomless  valleys.  We 
may  call  them  valleys,  but  this  does  not  express  the  idea;  they  are  gorges, 
deep  ravines  in  whose  gloomy  depths  rage  the  torrents  which  fall  from  the 
snowy  summits  of  the  Andes  down  toward  the  plain.  We  might  hunt  the 
world  over  for  a  better  example  of  the  power  of  running  water.  The 
whole  country  is  on  edge.  There  all  the  moisture  from  the  wet  air,  borne 
by  the  trade  winds  across  Brazil  from  the  distant  Atlantic,  is  wrung  by  the 
mountain  barrier  and  falls  in  almost  continual  rain. 

"  Near  the  summit  of  the  pass  only  the  lowest  and  scantiest  forms  of 
vegetable  life  are  seen.  In  a  single  day,  however,  even  by  the  slow  march 
of  weary  mules,  in  many  places  literally  stepping  '  downstairs '  from  stone 
to  stone,  we  drop  7,000  feet.  Here  the  forest  begins,  first  in  stunted  growths, 
and  then,  a  little  lower  down,  in  all  the  wild  luxuriance  of  the  tropics,  where 
moisture  never  fails.  The  lower  eastern  foot-hills  of  the  Andes  are  more 
heavily  watered  and  more  densely  overgrown  than  the  great  plain  farther 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  333 

down.  Here  is  a  land  drenched  in  rain  and  reeking  with  mists,  where  the 
bright  sun  is  a  surprise  and  a  joy  in  spite  of  his  heat.  In  these  dense  forests, 
with  their  twisting  vines  and  hanging  lianas,  a  man  without  a  path  can 
force  his  way  with  difficulty  a  mile  a  day.  ..." 

From  these  accounts,  and  from  the  greater  steepness  of  the 
eastern  side  of  the  Andes,  I  think  it  clear  that  the  perpetual  rain 
which  falls  there  sinks  down  as  if  the  country  were  overlaid  by  a 
deep  sea,  and  thus  in  effect  the  Andes  are  on  a  narrow  strip  between 
two  oceans.  Hence  the  terrific  effects  of  the  volcanic  forces,  which 
have  not  only  upraised  the  peaks  and  chains,  but  also  plateaus  like 
that  of  Titacaca.  While  the  western  ocean  furnished  the  forces 
for  the  original  uplift  of  the  chain,  the  reeking  tropical  rains  must 
have  augmented  these  forces  in  the  later  stages  of  the  Andean  de- 
velopment, and  this  amply  accounts  for  the  activity  of  the  volcanoes 
in  the  eastern  range.  These* volcanoes  might,  it  is  true,  be  accounted 
for  by  the  leakage  of  the  ocean,  yet  it  seems  probable  that  the 
enormous  surface  rainfall  can  hardly  fail  to  increase  the  volcanic 
violence  where  the  range  is  already  formed,  and  the  rocks  broken 
and  tilted  to  permit  of  a  maximum  seepage  of  the  ceaseless  tropical 
rains  which  constantly  soak  the  eastern  side  of  the  mountains. 

§  23.  On  the  process  involved  in  the  elevation  of  the  Alps. 

In  the  "Face  of  the  Earth,"  Vol.  II,  p.  121,  Professor  Suess 
shows  that  "  the  prevailing  tangential  movement  in  the  Alps  and 
Pyrenees  "  is  towards  the  north.  Thus  we  see  that  the  plains  of 
Lombardy  and  the  Valley  of  the  Po  constituted  the  sea  valley  which 
was  most  active  in  exerting  the  northern  tangential  thrusts  in  fold- 
ing the  Swiss  Alps.  Professor  Suess  (Vol.  I,  p.  274)  remarks  on 
the  similarity  of  the  Swabian-Franconian  sunken  area  north  of  the 
Alps,  and  the  depression  of  the  Adriatic  to  the  south.  An  exami- 
nation of  almost  any  good  map  will  convince  anyone  that  the 
Adriatic  once  covered  the  whole  of  the  valley  of  the  Po.  The 
maps  given  by  Reclus  in  his  large  work  "  La  Terre,"  p.  184,  show 
the  jutting  spurs  radiating  from  the  plains  of  Lombardy  into  the 
surrounding  mountains  on  all  sides.  This  result,  therefore,  is  a  very 
happy  confirmation  of  the  theory.  It  is  also  satisfactory  to  find 
that  the  Pennine  range  of  the  Alps,  nearest  the  valley  of  the  Po, 
including  Mt.  Blanc,  is  the  highest  of  these  great  mountains.  The 
highest  range  of  the  Himalayas,  including  Mt.  Everest,  also  stands 


334  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

nearest  the  valley  of  the  Ganges;  and  the  process  of  mountain- 
formation  seems  to  be  such  that  when  several  successive  ranges  are 
formed  and  completed  that  nearest  the  sea  is  the  highest,  probably 
because  the  forces  there  became  most  nearly  vertical. 

In  Vol.  II,  p.  552,  Professor  Suess  says :  "  As  a  result  of  tangen- 
tial thrusts  the  sediment  of  this  (Mediterranean)  Sea  was  folded  to- 
gether and  driven  upwards  as  a  great  mountain  range,  and  the  Alps 
have,  therefore,  been  described  as  a  compressed  sea." 

From  these  considerations,  it  is  obvious  that  the  Alps  were 
injected  from  several  sides,  but  especially  from  the  side  of  the 
valley  of  the  Po.  In  this  way,  the  successive  ranges  of  the  Alps 
were  formed,  probably  beginning  near  the  north,  and  working 
southward;  and  thus  we  see  that  the  valleys  of  Switzerland  are  the 
results  of  this  successive  wrinkling  of  the  crust.  Many  lakes  were 
formed  in  the  Alps,  and.  these  contributed  their  part  to  the  final 
shaping  of  the  contours  of  the  country.  As  the  country  was  sur- 
rounded by  seas  and  traversed  by  many  valleys  and  lakes,  all  of 
which  gave  the  water  access  to  the  bowels  of  the  earth  where  breaks 
of  the  rocks  were  once  started,  the  movements  finally  became  very 
complex,  and  hence  the  great  difficulty  of  unraveling  the  tangled 
skein  of  Alpine  development.  In  no  other  way  than  this  could  such 
a  system  of  mountains  have  arisen.  The  average  height  of  the 
Alpine  region  is  about  4,000  feet,  but  instead  of  a  level  tableland, 
it  is  a  mass  of  broken  chains  and  valleys,  showing  great  horizontal 
crumpling,  and  also  conspicuous  and  uneven  vertical  uplifts.  The 
Alps,  therefore,  afford  one  of  the  best  illustrations  of  the  theory. 
For  details  of  the  various  valleys  of  the  Alps,  and  the  great  faults 
which  mark  these  sunken  areas,  one  may  consult  Suess,  Vol.  I,  p. 
200,  et  seq. 

§24.  On  the  origin  of  the  Himalayas  and  of  the  Plateau  of  Tibet. 

If  we  study  the  general  character  of  the  Himalayas  by  means 
of  the  excellent  map  given  in  the  article,  "  India,"  Encyclopedia 
Britannica,  ninth  edition,  we  shall  find  that  the  most  conspicuous 
feature  of  this  great  chain  is  the  prominence  of  the  jutting  spurs  on 
the  south,  facing  the  ocean.  Perhaps  a  few  remarks  ought  to  be 
made  about  the  process  by  which  these  spurs  originate. 

We  have  seen  that  it  was  by  the  injection  of  lava  from  the  sea 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


335 


s 

p 
X) 


valleys  now  occupied  by  the  Ganges  and  Bramaputra  that  these 
mighty  mountains  were  upheaved.  In  this  process  there  would 
naturally  be  certain  paths  or  outlets  under  the  crust,  along  which 
the  lava  would  escape  most  easily ;  and  these  outlets  would  depend 
upon  the  upheaval  of  the  overlying  strata.  A  break  in  the  strata 
perpendicular  to  the  direction  of  the  chain  would  develop  into  a 


336  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

spur,1  because  the  upheaval  would  then  become  easy,  and  more  and 
more  lava  would  be  forced  into  the  outlet  thus  afforded.  By  means 
of  the  earthquakes  accompanying  the  expulsion  of  lava  from  the 
sea  valley  the  crust  is  broken  at  various  points,  and  thus  the  spurs 
are  gradually  developed.  It  is  noticeable  in  all  the  great  chains 
that  these  spurs  are  directed  towards  the  sea.  In  the  Himalayas, 
for  example,  they  are  on  the  convex  side,  while  in  the  Sierra  Ne- 
vadas  they  are  on  the  concave  side  of  the  chain ;  which  shows  that 
the  spurs  are  not  due  to  any  process  of  shrinkage  of  the  earth.  How- 
ever the  chains  may  curve,  the  spurs  will  be  found  towards  the  'sea 
valleys  from  which  the  expulsions  of  lava  have  taken  place.  This 
arrangement  of  the  spurs  shows  the  process  of  mountain  formation 
very  clearly. 

If  we  examine  the  map  of  Tibet  given  in  the  Encyclopedia 
Britannica,  ninth  edition,  we  shall  find  these  spurs  mainly  on  the 
outside  of  this  great  tableland.  It  was  therefore  injected  from  the 
seas  on  the  north  as  well  as  on  the  south;  for  the  Kuen  Lun  and 
Altin  Tagh  mountains  on  the  north  show  the  spurs  almost  as  dis- 
tinctly as  the  Himalayas,  on  the  south ;  and  on  the  north  of  Tibet 
the  spurs  point  towards  the  Arctic  ocean.  Tibet  was  thus  upheaved 
by  forces  injecting  this  great  tableland  on  all  sides.  It  is  thus  a 
very  elevated  plateau,  enclosed  by  terribly  high  mountains.  Before 
the  upheaval  had  attained  such  great  height,  no  doubt  the  enormous 
rainfall  produced  by  these  mountains,  and  hence  sinking  down  in 
the  faults  thus  opened  to  the  bowels  of  the  earth,  contributed  greatly 
to  the  uplifting  forces  due  to  the  surrounding  seas.  In  this  way  one 
may  account  easily  and  naturally  for  the  gradual  upheaval  of  the 
highest  plateau  in  the  world. 

The  forces  depending  on  the  valleys  of  the  Ganges  and  Brama- 
putra  are  still  active.  And  the  bones  of  elephants  and  rhinoceroses 
now  found  15,000  feet  above  the  sea,  an  elevation  at  which  these 
animals  could  not  possibly  have  lived  (cf.  article  "  Himalayas," 
Ency.  Brit.,  by  Gen.  Strachey),  show  that  the  vertical  uplift  of  Tibet 
took  place  in  comparatively  recent  geological  times.  When  this 
tableland  had  an  elevation  of  a  mile  or  less,  it  was  no  doubt  inhabited 

1  In  §  7  we  have  cited  Humboldt's  remarks  about  volcanoes  in  parallel 
ranges  being  connected  by  cross  ranges,  forming  mountain-nodes.  These 
are  similar  to  spurs,  and  hence  we  see  why  eruptions  occur  at  such  points. 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


337 


by  -numerous  large  quadrupeds ;  but  after  it  attained  an  altitude  of 
two  miles  they  had  naturally  deserted  it ;  and  now,  at  an  altitude  of 
nearly  three  miles  we  find  only  the  bones  to  show  that  it  was  once 
habitable  by  such  animals  as  now  flourish  in  the  low  plains  of  India. 


338  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  ,9t 

The  terrific  violence  of  the  earthquakes  which  are  still  felt  in  northern 
India  gives  us  an  idea  of  the  amazing  power  of  the  subterranean 
forces  by  which  this  great  uplift  was  produced.  In  elevating  the 
highest  mountains  of  the  world,  it  is  not  remarkable  that  they  also 
raised  the  highest  plateau. 

In  his  work  on  the  "  Face  of  the  Earth,"  Vol.  I,  p.  452,  Professor 
Suess  remarks  with  surprise  that  the  tangential  movement  shown 
by  the  mountains  has  opposite  direction  on  the  two  sides  of  the 
Bramaputra ;  this  confirms  the  present  theory  in  the  most  conclusive 
manner. 

§  25.  On  the  elevation  of  plateaus. 

It  will  be  seen  that  in  this  paper  we  abandon  contraction  as 
the  principal  modifying  cause  and  consider  only  the  light  matter 
proved  to  be  injected  under  mountains  and  narrow  plateaus  by  the 
power  of  steam,  which  gives  all  these  masses  a  substratum  of  honey- 
combed material  identical  with  the  lighter  lava  and  denser  pumice. 
That  this  material  now  lies  under  these  regions  of  greatest  elevation 
seems  certain,  and  in  place  of  the  contraction  theory,  we  may  sub- 
stitute that  of  steam  expansion  and  solidification,  upon  which  moun- 
tain building  depends.  This  is,  of  course,  effected  in  accordance 
with  Henry's  law  of  gaseous  absorption,  and  the  still  more  general 
law  that  matter  adapts  itself  to  the  pressure  to  which  it  is  subjected. 

It  will  be  seen  that  all  the  mathematical  reasoning  is  the  same 
whether  we  suppose  greater  contraction  under  the  oceans,  or  an 
actual  heaving  up  of  the  land  areas  by  the  injection  of  light  vol- 
canic material  more  or  less  full  of  bubbles,  which  decreases  the 
average  specific  gravity  of  the  land  and  mountains. 

Pendulum  observations  made  at  many  points  on  land  and  sea  also 
give  the  same  indication  as  respects  the  earth's  arrangement  of 
density ;  and  if  the  present  view  be  sound  the  interpretation  of  these 
observations  will  now  become  more  obvious. 

If  we  apply  the  foregoing  theory  to  a  narrow  plateau,  like  that 
of  Mexico,  which  is  a  uniform  tableland,  with  mountains  on  both 
sides,  it  will  become  evident  that  the  mountains  were  formed  when 
they  were  near  the  sea ;  and  that  when  the  shore  line  had  remained 
fixed  there  for  a  long  time  it  again  receded,  after  the  elevation  of 
the  mountains  and  the  tableland,  both  of  which  probably  were 


1906.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  339 


injected  with  light  volcanic  materials.  Hence  the  substratum  of 
such  a  plateau  is  composed  of  light  materials  similar  to  porous  lava 
and  pumice.  Only  a  few  mountains,  as  Orizaba,  Popocatapetl, 
Colima,  Jorullo,  experienced  such  violent  forces  as  to  come  to 
eruption,  but  the  materials  under  all  of  them  are  the  same.  The 
detritus  of  ashes  which  the  volcanoes  eject  is  nothing  but  pumice 
ground  to  dust  by  friction  and  explosive  violence.  It  is  obvious 
that  the  pumice,  ashes  and  other  volcanic  materials  are  not  made  at 
the  time  of  ejection,  but  are  always  in  store,  and  simply  happen  to 
be  thrown  out  of  any  mountain  which  experiences  eruption.  We 
may  in  all  probability  conclude  that  the  plateaus  of  Tibet,  Quito, 
Caxamarca,  Cuzco,  Titicaca,  and  other  elevated  regions  are  under- 
laid by  light  materials  like  that  thrown  from  volcanoes.  This  is 
certainly  true  of  the  great  ridges  of  the  Himalayas,  Alps,  Andes 
and  other  mountains  which  form  cordilleras.  In  fact,  the  ridges 
of  cordilleras  always  rest  upon  a  substratum  of  light  volcanic 
materials,  and  if  they  could  be  exploded  from  within  they  would 
dispense  ashes,  pumice  and  scoriae  as  abundantly  as  any  volcano. 
The  quantity  of  this  light  material  forced  up  under  the  ridges  of 
mountains  depends  upon  the  elevation,  and  breadth,  and  is  thus  enor- 
mous in  our  highest  ranges  like  the  Andes  and  Himalayas.  In  this 
way  we  may  explain  many  of  the  anomalies  of  geodesy,  and  pen- 
dulum observations,  without  any  other  hypothesis.  Is  not  the  ac- 
cordance of  observation  with  so  simple  a  theory  the  best  proof  that 
the  result  represents  a  general  law  of  nature  ? 

§  26.  On  the  theory  that  large  segments  of  the  lithosphere  act  as 
units  and  squeeze  those  segments  which  lie  between. 

In  the  new  work  on  "  Geology  "  by  Chamberlin  and  Salisbury, 
which  represents  the  trend  of  current  geological  thought,  the  authors 
adopt  a  subdivision  of  the  earth  into  large  segments  which  are  sup- 
posed to  act  as  units.  The  contraction  theory  is  the  basis  of  the 
reasoning,  and  part  of  the  discussion  is  as  follows : 

"  The  downward  movements  are  unquestionably  the  primary  ones,  and 
the  horizontal  ones  are  secondary  and  incidental.  The  fundamental  feature 
is  doubtless  central  condensation  actuated  by  gravity,  and  the  master  move- 
ments are  the  sinking  of  the  ocean-basins.  The  great  periodic  movements 
that  made  mountains  and  plateaus,  and  changed  the  capacity  of  the  ocean- 
basins,  probably  started  with  the  sinking  of  part  or  all  of  the  ocean-bottoms. 


340  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

In  the  greater  periodic  movements,  probably  all  the  basins  participated  more 
or  less,  but  some  seem  to  have  been  more  active  than  others.  For  example, 
in  the  last  great  mountain-making  period,  the  Pacific  basin  seems  to  have 
been  more  active  than  the  Atlantic,  while  in  the  similar  great  event  at  the 
close  of  the  Paleozoic,  the  opposite  seems  to  have  been  true.  The  squeezing 
up  of  the  continents  doubtless  took  place  simultaneously  with  the  settling  of 
the  basins.  The  true  conception  is  perhaps  that  the  ocean-basins  and  con- 
tinental platforms  are  but  the  surface  forms  of  great  segments  of  the  litho- 
sphere,  all  of  which  crowd  towards  the  center,  the  stronger  and  heavier  seg- 
ments taking  precedence  and  squeezing  the  weaker  and  lighter  ones  between 
them.  The  area  of  the  more  depressed  or  master  segments  is  almost  exactly 
twice  that  of  the  protruding  or  squeezed  ones.  This  estimate  includes  in  the 
latter  about  10,000,000  square  miles  now  covered  with  shallow  water.  The 
volume  of  the  hydrosphere  is  a  little  too  great  for  the  true  basins,  and  it 
runs  over,  covering  the  borders  of  the  continents.  The  amount  of  the  over- 
flow fluctuates  from  time  to  time,  and  may  be  neglected  in  a  study  of  the 
movements  and  deformation  of  the  lithosphere." 

Among  the  major  group  of  squeezed  segments  we  find:  (i) 
Eurasia,  (2)  Africa,  (3)  North  America,  (4)  South  America;  and 
the  minor  group  includes  Australia,  Antarctica,  the  East  Indian 
platform,  and  Greenland.  The  depressed  or  master  segments  are  the 
oceans:  (i)  The  Pacific,  (2)  the  Indian,  (3)  the  North  Atlantic, 
(4)  the  South  Atlantic ;  and  a  minor  group  of  smaller  seas,  as  the 
Arctic,  the  Mediterranean,  the  Caribbean,  and  the  chain  of  deep 
pits  between  the  Philippines  and  the  platform  of  Borneo. 

The  authors  discuss  the  crowding  of  these  segments  towards  the 
center  and  the  crumpling  which  follows  along  their  edges,  accom- 
panied by  fracture  and  slipping. 

"If  these  segments  be  regarded  as  the  great  integers  of  body-movement, 
two-thirds  of  them  taking  precedence  in  sinking  and  the  other  third  in  suffer- 
ing distortion,  it  is  easy  to  pass  to  the  conception  of  subsegments,  moving 
somewhat  differently  from  the  main  segments,  so  as  to  aid  in  their  adjust- 
ment to  one  another,  and  thus  to  the  conception  of  plateaus  and  deeps.  It 
is  easy  also  to  pass  to  the  conception  of  mutual  crowding  and  crumpling  at  the 
edges  of  these  segments,  accompanied  by  fracture  and  slipping.  These  con- 
ceptions perhaps  represent  the  true  relations  between  the  massive  move- 
ments of  the  abysmal  and  continental  segments,  as  well  as  the  less  massive 
plateau-forming  movements  and  the  mountain-forming  distortions.  The 
mountains  and  plateaus  are  probably  the  incidental  results  of  the  great 
abysmal  and  continental  readjustments. 

"  The  great  movements  are  probably  to  be  attributed  to  stresses  that 
gradually  accumulated  until  they  overcame  the  rigidity  of  the  thick  massive 
segments  involved,  and  forced  a  readjustment.  In  accumulating  these 
stresses,  some  local  yielding  on  weak  lines  and  at  special  points  was  an 


1906.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  341 

inevitable  incident  in  distributing  more  equably  the  accumulating  stresses. 
So,  also  the  first  great  readjustments  probably  left  many  local  strains  and 
unequal  stresses  which  gradually  eased  themselves  by  warpings,  minor  fault- 
ings,  etc.,  so  that  some  minor  movements  were  a  natural  sequence  of  the 
great  movements." 

From  these  citations  one  gets  a  good  idea  of  the  explanations 
heretofore  considered  most  plausible. 

Let  us  now  examine  this  reasoning  a  little  more  closely.  Is  it 
mechanically  conceivable  that  large  segments  of  the  lithosphere  should 
thus  act  together  as  units?  Would  not  such  action  imply  that  the 
the  earth  is  cut  deep  down  into  the  lithosphere  and  free  to  move 
along  the  boundaries  of  these  severed  segments?  If  the  lithosphere 
were  thus  cut  up  into  pieces,  and  all  the  segments  could  be  regarded 
as  solid,  with  abundant  lubricating  oil  between  them,  they  might 
by  their  mutual  gravity  crowd  towards  the  center,  and  possibly  the 
small  ones  would  be  squeezed  between  the  larger.  But  when  we 
recall  that  the  earth  is  not  cut  up  in  this  way,  with  oil  between  the 
pieces,  but  is  one  unbroken  mass,  it  is  clear  that  the  greatest  resis- 
tance would  arise  to  relative  motion  of  the  parts.  The  friction  of 
one  part  against  the  other  would  be  so  amazingly  great  that  no 
motion  would  take  place  at  the  supposed  joint.  Even  if  motion  oc- 
curred it  is  impossible  to  see  how  the  crust  could  be  crumpled  without 
producing  a  corresponding  condensation  of  the  matter  underlying 
the  folded  area,  the  density  of  which  would  thus  be  greatly  increased, 
in  some  cases  by  50  per  cent.  Now  geodetic  observations  show  that 
the  density  of  the  matter  under  the  mountains  not  only  is  not  greater 
than  the  average,  but  actually  less;  and  thus  we  see  that  the  folds 
of  the  crust  could  not  be  produced  in  this  way.  For  in  the  first 
place,  motion  could  not  take  place  on  account  of  friction;  and  in 
the  second  place,  if  it  took  place,  the  resulting  condensation  of  the 
underlying  matter  would  become  sensible  to  geodetic  measurement, 
which  is  contrary  to  observation. 

Is  it  not  therefore  impossible  to  entertain  the  doctrine  of  large  seg- 
ments of  the  lithosphere  moving  together  and  squeezing  others 
between  them?  Should  not  this  whole  theory,  along  with  the  hy- 
pothesis of  contraction  in  general,  be  entirely  given  up? 


342  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

VI.  CONFIRMATION  OF  THE  FOREGOING  THEORY  OF  MOUNTAIN 
BUILDING  BY  GEODESY. 

§  27.  General  considerations  on  the  attraction  of  mountains. 

If  the  theory  above  outlined  be  admissible  it  will  follow  that 
all  mountains  are  filled  with  light  material  like  porous  lava,  which 
was  originally  injected  as  hot  lava  under  great  steam  pressure,  full 
of  bubbles,  and  is  thus  similar  to  dense  pumice.  When  the  lava 
solidified,  the  bubbles  dried  up,  and  left  a  honeycombed  structure 
of  great  strength,  but  comparatively  small  weight.  The  deep  in- 
terior of  all  large  mountains  should  be  filled  with  material  of  this 
kind,  which  gives  strength,  but  has  low  density,  and  the  effect  of  its 
injection  is  to  reduce  the  average  density  of  the  mountain  below 
that  of  an  equal  mass  of  similar  material  taken  from  a  plain. 

It  is  remarkable  that  although  some  long  tunnels  through  moun- 
tain chains  have  been  bored  by  human  effort,  none  of  them  has  gone 
more  than  a  mile  or  so  deep,  and  thus  all  are  too  shallow  to  give  us 
any  experimental  knowledge  of  the  materials  in  the  depths  of  the 
mountains.  No  large  mountain  has  been  eroded  to  great  depth, 
and  hence  our  only  knowledge  of  the  interior  of  mountains  is  de- 
rived from  volcanic  action,  which  blows  out  the  inner  portions  of 
some  of  them.  The  mountains  which  happen  to  break  out  as  vol- 
canoes, either  because  the  subterranean  steam  pressure  is  suddenly 
applied  and  abnormally  great,  or  because  they  are  weak  in  some 
point  of  their  construction,  are  obviously  not  different  from  ordi- 
nary chains  and  peaks,  until  after  they  break  forth. 

Eruptions  are  always  accompanied  by  violent  earthquakes,  and 
a  mountain  does  not  take  fire  and  form  ashes  and  cinders  by  burn- 
ing, but  blows  out  the  volcanic  materials  already  stored  up  in  vast 
quantities.  Thus  we  naturally  infer  that  all  mountains  are  essen- 
tially alike,  but  we  are  never  able  to  see  the  inner  contents  except 
of  the  few  of  them  which  have  become  volcanoes.  And  if  we  are 
able  to  explore  the  interior  of  all  mountains,  it  is  only  by  studying 
the  materials  expelled  from  volcanoes  by  the  explosive  power  of 
steam.  It  is  doubtful  if  even  the  oldest  mountains  show  erosion  a 
mile  deep,  and  hence  we  cannot  penetrate  the  earth's  crust  to  any 
depth  except  by  an  analysis  of  the  materials  which  come  out  of  the 
mountains  after  they  are  blown  open  in  eruption.  It  is  scarcely 


i9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  343 


necessary  to  add  that  new  ashes,  cinders,  scoriae,  pumice  and  other 
volcanic  materials  are  not  as  a  whole  red  hot,  and  therefore  the  bulk 
of  them  is  not  formed  at  the  time  of  the  first  volcanic  outbreak. 
They  have  been  resting  quietly  under  the  mountain  for  immeasurable 
ages,  and  one  cannot  doubt  that  they  exist  in  all  mountains. 

It  is  unfortunate  that  a  custom  has  arisen  of  speaking  of  vol- 
canic action  as  essentially  superficial.  While  it  cannot  be  said  to 
have  any  fixed  depth,  and  in  many  cases  may  not  be  extremely  deep, 
it  is  safe  to  say  that,  as  a  general  rule,  it  is  by  no  means  very 
shallow.  On  the  average  the  depth  is  at  least  of  the  same  order  as 
the  height  of  the  mountains,  plus  the  depth  of  the  adjacent  sea. 
There  is  every  reason  to  suppose  the  forces  which  pushed  up  the 
Andes  and  keeps  some  of  them  in  active  eruption  arises  from  about 
the  same  depth  as  the  most  violent  earthquakes  which  visit  that 
region.  Only  a  few  of  the  peaks  of  the  Andes  have  become  vol- 
canoes, but  some  of  them,  as  Aconcagua,  in  Chili,  Gualateiri  and 
Sahama,  of  the  Sorata  Range  in  Bolivia,  and  Cotopaxi  and  its 
associates  near  Quito  in  Ecuador  are  all  very  high ;  and  the  ejection 
of  materials  at  that  height  requires  deep-seated  and  most  tremen- 
dous forces.  Yet  obviously  only  a  small  part  of  the  energy  origi- 
nating under  the  base  of  a  volcano  has  been  spent  in  ejecting  lava, 
rocks,  ashes  and  cinders;  a  very  large  part  of  the  energy  exerted 
from  below  has  been  spent  in  raising  the  sides  of  the  mountain  before 
eruption  broke  out  at  the  top. 

We  may  then  consider  all  mountains  to  be  made  up  internally  of 
light  material  like  that  blown  out  of  volcanoes.  Chimborazo,  for 
example,  may  never  have  had  an  eruption,  and  yet  it  is  impossible 
to  believe  that  its  constitution  is  essentially  different  from  that  of 
the  neighboring  mountains  of  Cotopaxi,  Pinchinchi,  Antisana, 
Tunguragua,  Sangay,  and  Cayambe,  all  of  which  are  volcanoes. 

Now  it  is  a  very  remarkable  fact  of  observation  that  geodetic 
researches  in  many  countries,  and  pretty  much  ever  since  the  ex- 
periments of  Bouguer  and  La  Condamaine  on  Chimborazo  in  the 
year  1738,  have  tended  to  show  that  the  matter  under  the  roots  of  a 
great  mountain  is  lighter  than  the  average  matter  of  the  adjacent 
plain.  In  their  experiments  on  the  deviation  of  the  plumb  line 
near  Chimborazo  the  existence  of  great  cavities  in  this  colossal 

PROC.  AMER.  PHIL.  SOC.,  XLV.    184  V,  PRINTED  FEBRUARY  23,   1907. 


344  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  ,9, 

trachytic  mountain  was  suspected  by  Bouguer  and  La  Condamaine, 
though,  as  Humboldt  remarks,  the  evidence  was  unsatisfactory 
(Cosmos,  Vol.  V,  p.  30).  Yet  the  foregoing  theory  enables  us  to 
recognize  that  the  similar  widely  extended  indications  of  modern 
geodesy  can  hardly  fail  to  be  real;  and  according  to  the  principle 
of  continuity  the  law  thus  found  for  certain  mountains  must  be  held 
to  be  general  for  all  the  great  peaks  and  chains  of  our  globe.  In 
fact  the  satisfactory  explanation  of  this  long-standing  geodetic  prob- 
lem would  seem  to  be  one  of  the  strongest  arguments  which  could 
be  adduced  in  favor  of  the  truth  of  the  present  theory  of  mountain 
constitution  and  formation.  For  the  facts  of  geodesy  are  based  upon 
exact  observation  and  experiment,  and  unbiased  by  any  theory ;  and 
yet  they  become  intelligible  only  when  interpreted  by  means  of  a 
general  theory  like  the  present.  The  support  thus  furnished  by  a 
wide  body  of  geodetical  facts  would  seem  to  place  the  theory  of 
mountain  constitution  on  a  basis  where  it  may  become  a  useful 
adjunct  to  the  principles  of  geodetic  measurement. 

Probably  no  measurements  involving  long  distances  upon  the 
earth  have  so  high  an  order  of  accuracy  as  those  of  geodesy.  Is  it 
too  much  to  hope  that  the  principle  of  mountain  constitution  here 
outlined  may  become  the  means  of  still  greater  refinement,  in  the 
triangulation  of  the  earth's  surface  ? 

In  his  well-known  work  on  the  "  Figure  of  the  Earth,"  x  Pratt 
announces  a  proposition : 

"  To  deduce  from  the  previous  calculations  some  probable  conclusions  re- 
garding the  constitution  of  the  earth's  crust.  The  first  thing  to  be  observed 
in  the  results  given  in  the  last  paragraph  is  the  very  small  amount  of  the 
resulting  deflection  at  the  two  extremities  of  the  Indian  Arc — Punnae  close  to 
Cape  Comorin,  and  Kaliana  the  nearest  station  to  the  Himalayan  Mountains; 
whereas  the  effect  of  the  Ocean  and  Mountains  has  been  shown  to  be  very 
large.  This  shows  that  the  effect  of  variations  of  density  in  the  crust  must 
be  very  great,  in  order  to  bring  about  this  near  compensation.  In  fact  the 
density  of  the  crust  beneath  the  mountains  must  be  less  than  that  below  the 
plains,  and  still  less  than  that  below  the  ocean-bed." 

Again  :2 

"  The  circumstance  already  noticed,  that  at  seven  coast  stations  out  of 
thirteen  the  deflection  is  toward  the  sea,  seems  to  bear  testimony  to  the  truth 
of  the  theory,  that  the  crust  below  the  ocean  must  have  undergone  greater 

"  Figure  of  the  Earth,"  3d  edition,  p.  134. 
2  Ibid.,  p.  136. 


I9o6.]  v  SEE— THE  CAUSE  OF  EARTHQUAKES.  345 

contraction  than  other  parts.  The  deflection  toward  the  land  at  the  other 
six  coast-stations  can  of  course  easily  be  understood  without  at  all  calling  in 
question  the  theory.  The  proximity  of  the  land  may  easily  be  conceived 
sufficient  to  counteract  any  effect  of  the  more  distant  parts  of  the  ocean.  It 
is  the  fact  of  even  some  of  the  deflections  being  toward  the  sea,  that  bears 
testimony  to  the  theory,  while  the  others  offer  no  argument  to  the  contrary." 
"The  least,  then,  that  can  be  gathered  from  the  deflections  of  these 
coast-stations  is,  that  they  present  no  obstacle  to  the  theory  so  remakably 
suggested  by  the  facts  brought  to  light  in  India,  viz.,  that  mountain-regions 
and  oceans  on  a  large  scale  have  been  produced  by  the  contraction  of  the 
materials,  as  the  surface  of  the  earth  has  passed  from  a  fluid  state  to  a  con- 
dition of  solidity — the  amount  of  contraction  beneath  the  mountain-region 
having  been  less  than  that  beneath  the  ordinary  surface,  and  still  less  than 
that  beneath  the  ocean-bed,  by  which  process  the  hollows  have  been  produced 
into  which  the  ocean  has  flowed.  In  fact  the  testimony  of  these  coast-sta- 
tions is  rather  in  favour  of  the  theory,  as  they  seem  to  indicate,  by  excess  of 
attraction  towards  the  sea,  that  the  contraction  of  the  crust  beneath  the 
ocean  has  gone  on  increasing  in  some  instances  still  further  since  the  crust 
became  too  thick  to  be  influenced  by  the  principles  of  floatation,  and  that 
an  additional  flow  of  water  into  the  increasing  hollow  has  increased  the 
amount  of  attraction  upon  stations  on  its  shores."  1 

We  have  quoted  this  paragraph  to  recall  how  geodesists  have 
heretofore  attempted  to  explain  the  comparative  lightness  of  the 
matter  beneath  the  mountains,  and  the  greater  density  of  that 
beneath  the  plains  and  especially  beneath  the  sea. 

Pratt  elsewhere  says  that  the  hidden  cause  of  the  deflection  of 
the  plumb  line  between  the  mountain  masses  on  the  north  and  the 
Indian  Ocean  on  the  south  "  may  lie  below,  in  the  variations  of  the 
density  of  the  earth's  crust."  2  He  then  examines  various  arrange- 
ments of  density,  and  finally  calculates  by  three  hypotheses  that 
the  sea  level  in  Great  Britain  stands  at  a  mean  height  of  1,567 
feet  higher  than  it  would  if  the  ocean  hemisphere  with  pole  in  New 
Zealand  became  land,  other  things  remaining  equal. 

§  28.  Pratt' 's  theorem  on  the  equilibrium  of  the  earth  between  the 
land  and  water  hemispheres? 

"There  is  no  doubt  that  the  solid  parts  of  the  earth's  crust,  beneath  the 
Pacific  Ocean  must  be  denser  than  in  the  corresponding  parts  on  the  op- 
posite side,  otherwise  the  ocean  would  flow  away  to  the  other  parts  of  the 
earth.  The  following  reasoning  will  explain  this.  Suppose  the  earth  to  be 
a  sphere.  Through  any  point  on  it  suppose  a  surface  drawn  separating  a 

1  "  Figure  of  the  Earth,"  3d  edition,  p.  137. 

2  Ibid.,  p.  148. 

3  Ibid.,  pp.  159-160. 


346  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

thin  portion  on  the  right  hand  and  through  the  same  point  a  similar  surface 
separating  a  like  portion  on  the  left.  The  sphere  consists,  then,  of  three 
parts,  the  middle  portion  being  of  a  symmetrical  form  and  attracting  the  point 
in  the  direction  of  the  radius,  and  the  two  slender  slices  attracting  it  equally 
to  the  right  and  left  of  that  radius.  If  one  of  these  slices  became  fluid  and  of 
less  density  than  the  other,  its  attraction  would  be  overcome  by  that  of  the 
other,  and  the  fluid  would  be  drawn  away  to  the  other  parts  of  the  sphere. 

"  It  does  not  follow  that  the  whole  of  the  fluid  would  be  drawn  over.  The 
above  process  would  go  in  till  the  surface  of  the  fluid  at  the  circumference  of 
the  slice  had  become  so  inclined  as  to  be  at  right  angles  to  the  direction  of 
the  resultant  attraction  of  the  whole  mass,  solid  and  fluid.  If,  however,  a 
narrow  channel  were  cut  through  this  circumference  (which  would  otherwise 
act  as  an  embankment)  the  whole  of  the  water  would  be  drawn  off. 

"  Now  in  the  case  of  the  earth  there  is  a  channel  opening  a  passage  from 
the  New  Zealand  hemisphere  into  the  opposite  one,  viz.,  the  North  -and  South 
Atlantic,  and  yet  the  ocean  remains  in  that  hemisphere.  There  must,  there- 
fore, be  some  excess  of  matter  in  the  solid  parts  of  the  earth  between  the 
Pacific  Ocean  and  the  earth's  centre  which  retains  the  water  in  its  place. 
This  effect  may  be  produced  in  an  infinite  variety  of  ways;  and  therefore, 
without  data,  it  is  useless  to  speculate  regarding  the  arrangement  of  matter 
which  actually  exists  in  the  solid  parts  below." 

Pratt  then  discusses  the  original  fluidity  of  the  earth,  and  says 
finally : 

"The  conclusion  at  which  we  have  arrived  in  Art.  132,  that  the  parts 
of  the  crust  below  the  more  elevated  regions  are  of  less  density,  and  the 
parts  beneath  the  depressed  regions  in  the  oceans  are  of  greater  density  than 
the  average  portions  of  the  surface,  seems  to  bear  additional  testimony  to  the 
fluid  theory.  For  it  shows,  that  notwithstanding  the  varied  surface,  seen 
at  present  in  mountains  and  oceans,  the  amount  of  matter  in  a  vertical 
prism  drawn  down  at  various  places  to  any  given  spheroidal  stratum  is  the 
same  although  its  length  varies  from  place  to  place  as  the  earth's  contour 
varies.  No  better  explanation  of  this  phenomenon  can  be  conceived  than 
that  which  the  fluid  hypothesis  furnishes;  viz.,  that  these  prisms  though  now 
of  different  lengths,  were,  when  the  crust  was  fluid,  of  the  same  length ;  and 
as  their  lengths  are  now  various  simply  from  the  fact  that  the  surface  in 
solidifying  has  contracted  unequally,  of  course  the  amount  of  matter  which 
they  contain  is  the  same  in  all  of  tljem."1 

The  views  here  expressed  are  very  generally  recognized  by 
geodesists,  and  have  been  treated  in  different  ways  by  Clarke, 
Tisserand,  Helmert,  and  other  leading  authorities. 

§  29.  Results  obtained  by  the  United  States  Coast  and  Geodetic 
Survey  from  recent  researches  on  the  average  depth  of  isostatic 
compensation. 

1 "  Figure  of  the  Earth,"  3d  edition,  p.  162. 


I9o6.j  SEE— THE  CAUSE  OF  EARTHQUAKES.  347 

With  the  approval  of  Dr.  O.  H.  Tittman,  superintendent,  Mr. 
J.  F.  Hayford  has  recently  presented  to  the  Washington  Academy  of 
Sciences  and  published  in  the  Proceedings  for  May  18,  a  valuable 
summary  of  the  results  deduced  from  the  geodetic  operations  in 
the  United  States.  He  has  discussed  with  care  the  long  series  of 
deflections  of  the  vertical  as  determined  by  Clarke's  Standard 
Spheroid  of  1866,  which  has  been  found  to  fit  best  for  the  area 
covered  by  the  United  States,  and  determined  the  depths  at  which 
isostatic  compensation  takes  place.  By  five  solutions  of  the  prob- 
lem he  finds  the  residuals  least  for  a  depth  of  71  miles.  Some  of  the 
conclusions  are  stated  thus : 

"  The  evidence  shows  clearly  and  decisively  that  the  assumption  of  com- 
plete isostatic  compensation  within  the  depth  of  71  miles  is  a  comparatively 
close  approximation  to  the  truth,  that  the  assumption  of  extreme  rigidity  is 
far  from  the  truth — that  the  United  States  is  not  maintained  in  its  position 
above  the  sea  level  by  the  rigidity  of  the  earth,  but  is,  in  the  main,  buoyed  up, 
floated,  upon  underlying  material  of  deficient  density. 

"The  conclusions  just  stated  were  based  upon  the  507  residuals  con- 
sidered as  one  group.  The  residuals  have  been  examined  in  separate  groups 
of  25,  each  group  covering  a  small  region.  Not  a  single  group  of  25  con- 
tradicts the  conclusion  just  stated. 

"It  is  certain  that  for  the  United  States  and  adjacent  regions  including 
oceans,  the  isostatic  compensation  is  more  than  two-thirds  complete — perhaps 
much  more. 

"  The  departure  from  perfect  compensation  may  be,  in  some  regions,  in 
the  direction  of  overcompensation  rather  than  undercompensation  but  in 
either  case  the  departure  from  perfect  compensation  is  less  than  one-third. 

"  In  terms  of  stresses,  it  is  safe  to  say  that  these  geodetic  observations 
prove  that  the  actual  stresses  in  and  about  the  United  States  have  been  so 
reduced  by  isostatic  adjustment  that  they  are  less  than  one-tenth  as  great 
as  they  would  be  if  the  continent  were  maintained  in  its  elevated  position, 
and  the  ocean  floor  maintained  in  its  depressed  position,  by  the  rigidity  of 
the  earth." 

Mr.  Hayford  assumed  that  the  compensation  is  uniformly  dis- 
tributed with  respect  to  the  depth,  but  he  remarks  that  this  is  only  a 
convenient  working  hypothesis.  Pendulum  observations  combined 
with  deflection  observations,  he  thinks,  may  furnish  the  means  of 
detecting  the  distribution  of  compensation.  Assuming  that  the 
compensation  all  occurs  within  a  stratum  10  miles  thick,  the  bot- 
tom of  the  stratum  of  isostatic  compensation  comes  out  37  miles. 
Mr.  Hayford,  however,  prefers  the  depth  of  71  mijes,  though  he 
adds  that  it  rests  upon  an  insecure  foundation.  He  concurs  with 


348  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

the  view  now  generally  held  that  compensation  is  always  going  on, 
through  the  changes  of  levels  due  to  erosion  and  other  causes. 
Mr.  Hayford's  paper  is  extremely  important  in  showing  that  the 
depth  of  compensation  is  not  great,  and  the  principal  inequalities 
of  density  are  essentially  limited  to  the  earth's  crust,  complete  aver- 
age compensation  for  the  whole  country  occurring  within  about 
three  or  four  times  that  depth.  The  result,  therefore,  accords  well 
with  the  views  developed  in  the  present  investigation.  In  his  dis- 
cussion of  Hayford's  paper,  Major  Button,  who  was  present,  re- 
marked that  "  the  heavy  masses  of  sediment  which  are  formed  upon 
the  bottom  of  the  sea  can,  I  conceive,  only  be  elevated  by  a  positive 
uplifting  force." 

VII.  THE  ORIGIN  OF  ISLANDS  AND  THE  SECULAR  MOVEMENT  OF 

THE  STRAND. 

§  30.  Submarine  earthquakes  and  volcanoes. 

The  eruption  of  volcanoes  from  the  sea  was  noted  by  the  Greeks, 
as  we  learn  from  Aristotle  (Meteor.,  ii,  8,  17-19),  quoted  by  Hum- 
boldt  in  Cosmos,  Vol.  I,  p.  240,  Bohn's  translation: 

"The  heaving  of  the  earth  does  not  cease  till  the  wind  (dvquof)  which 
occasions  the  shocks  has  made  its  escape  into  the  crust  of  the  earth.  It  is 
not  long  ago  since  this  actually  happened  at  Heraclea  in  Pontus,  and  a 
similar  event  formerly  occurred  at  Hiera,  one  of  the  Aeolian  Islands.  A  por- 
tion of  the  earth  swelled  up,  and  with  loud  noise  rose  into  the  form  of  a  hill, 
till  the  mighty  urging  blast  (Trvev^a)  found  an  outlet,  and  ejected  sparks  and 
ashes  which  covered  the  neighborhood  of  Lapari,  and  even  extended  to  sev- 
eral Italian  cities." 

Strabo  (lib.  i,  p.  59)  describes  the  naming  eruption  observed  at 
Methone  in  the  year  282  B.  C,  near  the  town  in  the  Bay  of  Her- 
mione,  saying  a  fiery  mountain  arose  seven  stadia  in  height,  inac- 
cessible by  day  on  account  of  its  heat  and  sulphurous  flames,  but 
emitting  an  agreeable  odor  at  night.  It  was  so  hot  that  the  sea 
boiled  for  a  distance  of  five  stadia,  and  was  turbid  and  filled  with 
detached  masses  of  rock  for  full  twenty  stadia.  This  eruption  is 
also  mentioned  by  Ovid1  (Metam.,  xv). 

"  Near  Troezen  is  a  tumulus,  steep  and  devoid  of  trees,  once  a  plain, 
now  a  mountain.  The  vapours  enclosed  in  dark  caverns  in  vain  seek  a  pas- 
sage by  which  they  may  escape.  The  heaving  earth,  inflated  by  the  force 
of  the  compressed  vapours,  expands  like  a  bladder  filled  with  air,  or  like  a 
goat  skin.  The  ground  has  remained  thus  inflated  and  the  high  projecting 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  349 

Another  island  eruption  on  Thera  occurred  forty-five  years 
later,  and  thet  ancients  were  perhaps  familiar  with  additional  sub- 
marine outbreaks  on  the  Italian  coast ;  otherwise  probably  few  if  any 
more  submarine  volcanoes  were  noted  till  modern  times.1 

A  few  submarine  volcanoes,  either  new  or  of  recent  origin,  were 
noted  by  the  early  navigators,  but  the  phenomenon  of  volcanic 
upheavals  at  sea  did  not  attract  much  attention  till  the  time  of 
Humboldt,  who  made  a  careful  study  of  all  such  outbursts.  In  the 
Cosmos  Humboldt  mentions  five  submarine  volcanoes  which  ap- 
peared in  the  first  half  of  the  nineteenth  century.  Probably  it 
would  be  difficult  to  give  a  complete  list  of  all  the  submarine  vol- 
canoes which  have  ever  appeared,  as  the  records  are  widely  scat- 
tered, and  to  be  of  value  would  have  to  be  critically  examined  in 
each  case.  It  is  also  clear  that  more  such  volcanoes  would  now  be 
noticed  than  in  former  centuries,  because  the  travel  and  explora- 
tion of  the  sea  is  more  extensive  than  in  former  ages ;  yet  even  now 
great  areas  of  the  ocean  are  quite  seldom  visited  by  ships,  so  that 
the  world  knows  little  or  nothing  of  what  is  going  on  in  a  large  part 
of  the  globe.  If  a  submarine  volcano  of  short  duration  should  be 
upheaved,  it  might  again  disappear  and  leave  no  record  of  its  ex- 
istence. Numerous  islands  are  also  raised  in  the  sea  without  visible 
volcanic  outlets.  The  average  number  of  submarine  volcanoes 
upheaved  in  a  century,  if  careful  watch  could  be  kept  on  the  oceans 
throughout  the  world,  might  prove  to  be  something  like  one  every 
two  years,  or  50  in  a  century.  This,  however,  is  merely  the  num- 
ber of  peaks  which  would  raise  their  heads  above  the  water.  As 
most  of  the  oceans  are  much  too  deep  for  them  to  show  above  the 
sea  level,  it  is  clear  that  the  number  which  remain  covered  by  the 
sea  is  very  much  greater  than  those  which  rise  into  view,  in  a  ratio 
of  perhaps  something  like  20  to  I.  Thus  in  the  whole  earth  there 
may  be,  and  probably  are,  1,000  submarine  volcanoes  erupted  in  a 
century,  or  an  average  of  ten  in  a  year.  In  this  way  we  may  ex- 
plain some  of  the  great  sea  waves  so  often  encountered  by  navi- 
gators, and  frequently  noted  by  the  tide  gauges  in  civilized  coun- 

eminence    has    been    solidified   by    time    into    a   naked    rock"    (Humboldt's, 
Cosmos,  Vol.  I,  p.  239). 

1  The  list  island  chances  in  the  Mediterranean  recorded  by  Pliny  in  his 
Natural  History  is  quite  impressive  (cf.  Lib.  ii.). 


350  SEE—  THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

tries.  Not  all  volcanoes  thus  upheaved  would  be  sufficiently  large 
and  energetic  in  their  action  to  be  widely  or  distinctly  felt,  because 
some  would  be  small  and  slow  in  their  action  and  hence  produce 
no  sensible  sea  waves.  Yet  when  we  consider  how  much  of  the  sea 
passes  unobserved,  and  how  many  sea  waves  actually  are  reported, 
an  average  of  ten  submarine  volcanoes  per  year  does  not  seem  too 
high  an  estimate.  Those  which  are  small  and  in  deep  water  will 
escape  notice  entirely;  and  in.midocean  none  except  the  powerful 
eruptions  could  make  themselves  felt,  because  there  is  no  means  of 
detecting  a  disturbance  of  sea  level,  unless  it  happens  to  be  large 
enough  to  disturb  a  passing  ship. 

In  his  well-known  article  on  "  Geology  "  in  the  Encyclopedia 
Britannica,  ninth  edition,  Sir  Archibald  Geikie  says  : 

"At  the  Hawaii  Islands,  on  25th  February,  1877,  masses  of  pumice, 
during  a  submarine  volcanic  explosion,  were  ejected  to  the  surface,  one  of 
which  struck  the  bottom  of  a  boat  with  considerable  violence  and  then  floated. 
At  the  same  time  when  we  reflect  to  what  a  considerable  extent  the  bottom 
of  the  great  ocean  basins  is  dotted  over  with  volcanic  cones,  rising  often 
solitary  from  profound  depths,  we  can  understand  how  large  a  proportion  of 
the  actual  eruptions  may  take  place  under  the  sea.  The  foundations  of  these 
volcanic  islands  doubtless  consist  of  submarine  lavas  and  fragmentary  ma- 
terials, which,  in  each  case,  continued  to  accumulate  to  a  height  of  two  or 
three  miles,  until  the  pile  reached  the  surface  of  the  water  and  the  phenomena 
became  subaerial.  The  immense  abundance  and  wide  diffusion  of  volcanic 
detritus  over  the  bottom  of  the  Pacific  and  Atlantic  Oceans,  even  at  dis- 
tances remote  from  land,  as  has  been  made  known  by  the  voyage  of  the 
'  Challenger/  may  indicate  the  prevalence  and  persistence  of  submarine 
volcanic  action,  though  at  the  same  time,  it  must  be  admitted  that  an  ex- 
tensive diffusion  of  volcanic  debris  from  the  islands  is  effected  by  winds 
and  ocean-currents." 


^  evidence  therefore  that  the  sea  bottom  is  very  leaky  and  in 
a  constant  state  of  eruption  in  many  places  seems  conclusive.  In 
other  places  very  few  eruptions  occur,  because  the  underlying  rocks 
are  less  leaky  and  the  sea  is  too  shallow  to  exert  much  pressure. 
The  number  of  earthquakes  under  the  sea  must  be  much  greater 
than  those  on  land,  area  for  area  ;  but  here  again  few  are  observed, 
and  still  fewer  traced  to  their  centers,  because  the  data  are  in- 
sufficient. 

It  is   fully  recognized,  however,  that  many  submarine   earth- 
quakes occur  off  the  east  coast  of  Japan  and  the  Philippines,  in  the 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  351 

Aleutian  Islands,  off  the  coast  of  Peru  and  Chili,  near  St.  Paul's 
Island  in  the  Atlantic,  the  Antilles  and  the  East  Indies.  And 
while  the  investigation  of  these  phenomena  is  still  in  its  infancy, 
we  may  be  sure  they  are  of  wide  and  universal  distribution,  espe- 
cially in  the  deepest  oceans,  where  the  shores  are  steep  and  broken, 
as  in  volcanic  regions.  The  southern  Pacific  Ocean,  where  so 
many  volcanic  islands  exist,  must  be  a  prolific  but  unexplored 
center  of  such  disturbances. 

§  31.  Views  of  Charles  Darwin  on  the  distribution  of  volcanic 
islands. 

"  During  my  investigations  on  coral  reefs,  I  had  occasion  to  consult  the 
works  of  many  voyagers,  and  I  was  invariably  struck  with  the  fact  that  with 
rare  exceptions,  the  innumerable  islands  scattered  throughout  the  Pacific, 
Indian,  and  Atlantic  Oceans,  were  composed  either  of  volcanic  or  of 
modern  coral-rocks.  It  would  be  tedious  to  give  a  long  catalogue  of  all 
the  volcanic  islands,  but  the  exceptions  I  have  found  are  easily  enumerated: 
In  the  Atlantic  we  have  St.  Paul's  Rock,  described  in  this  volume,  and  the 
Falkland  Islands,  composed  of  quartz  and  clay  slate ;  but  these  latter 
islands  are  of  considerable  size,  and  lie  not  very  far  from  the  South  Amer- 
ican coast:  in  the  Indian  Ocean,  the  Seychelles  (situated  in  a  line  prolonged 
from  Madagascar)  consists  of  granite  and  quartz :  in  the  Pacific  Ocean,  New 
Caledonia,  an  island  of  large  size,  belongs  (as  far  as  is  known)  to  the 
primary  class.  New  Zealand,  which  contains  much  volcanic  rock  and  some 
active  volcanoes,  from  its  size  cannot  be  classed  with  the  small  islands, 
which  we  are  now  considering.  The  presence  of  a  small  quantity  of  non- 
volcanic  rock  as  of  clay  slate  on  three  of  the  Azores,  or  of  the  tertiary  lime- 
stone of  Maderia,  or  of  clay-slate  at  Chatham  Island  in  the  Pacific,  or  of 
lignite  at  Kerguelen  land,  ought  not  to  exclude  such  islands  or  achipelagoes, 
if  formed  chiefly  of  erupted  matter,  from  the  volcanic  class. 

"The  composition  of  the  numerous  islands  scattered  through  the  great 
oceans  with  such  rare  exceptions  volcanic,  is  evidently  an  extension  of  that 
law,  and  the  effect  of  the  same  causes,  whether  chemical  or  mechanical,  from 
which  it  results,  that  a  vast  majority  of  the  valcanoes  now  in  action  stand 
either  as  islands  in  the  sea,  or  near  its  shores.  This  fact  of  the  oceanic  is- 
lands being  so  generally  volcanic  is  also  interesting  in  relation  to  the  nature 
of  the  mountain-chains  on  our  continents,  which  are  comparatively  seldom 
volcanic;  and  yet  we  are  led  to  suppose  that  where  our  continents  now 
stand  an  ocean  once  extended.  Do  volcanic  eruptions,  we  may  ask,  reach 
the  surface  more  readily  through  fissures  formed  during  the  first  stages  of  the 
conversion  of  the  bed  of  the  ocean  into  a  tract  of  land  ?  " * 

In  connection  with  the  above  views  of  Darwin  it  should  be  noted 
that  not  all  of  the  islands  which  are  upheaved  in  the  sea  could  be 
1  "  Geological  Observations  on  Volcanic  Islands,"  chapter  VI. 


352  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

expected  to  pour  forth  molten  rock  so  as  to  give  above  the  water 
a  volcanic  aspect.  In  some  cases  the  islands  would  be  raised  with- 
out eruption  breaking  out  at  all,  while  in  others  the  eruptive  out- 
breaks would  occur  beneath  the  sea,  and  the  surface  appearance  of 
such  islands  would  be  non-volcanic. 

§  32.  Dr.  Rudolph's  views  on  submarine  earthquakes  and  erup- 
tions. 

In  the  first  volumes  of  "  Beitrage  zur  Geophysik  "  (especially 
Vols.  I  and  II)  Dr.  E.  Rudolph  has  several  elaborate  papers  dealing 
with  the  subject  of  submarine  earthquakes  and  eruptions  in  an 
exhaustive  manner.  The  large  catalogues  of  such  phenomena  col- 
lected in  this  careful  inquiry  are  certainly  impressive,  and  the 
results  of  Dr.  Rudolph's  investigations  may  be  said  to  confirm  the 
view  here  taken  that  the  sea  bottom  is  in  a  constant  state  of  vol- 
canic disturbance.  These  disturbances  are  in  fact  so  frequent  that 
a  similar  view  is  held  by  many  experienced  navigators  as  the  result 
of  their  own  observations.  What  explanation  can  be  given  for  such 
phenomena  except  the  penetration  of  the  sea  water  into  the  earth's 
crust?  Volcanic  outbreaks  never  occur  except  along  the  shores 
or  under  the  sea.  The  significance  of  these  disturbances  of  the  sea 
bottom  and  their  connection  with  the  formation  of  islands  seems 
therefore  obvious.  In  the  "  Face  of  the  Earth,"  Vol.  I,  p.  61, 
Professor  Suess  remarks  on  the  calm  attitude  of  the  scholar  in  the 
midst  of  dangerous  natural  phenomena,  and  gives  the  following 
interesting  account  of  Apollonius  of  Tyana: 

"  In  the  year  62  or  65  A.  D.  Apollonius  of  Tyana  was  on  the  island  of 
Crete.  He  was  on  that  coast  of  the  island  which  is  washed  by  the  Libyan 
Sea,  on  a  promontory  in  the  neighborhood  of  Phastus,  and  was  engaged  in 
conversation  with  a  number  of  men  who  had  come  to  do  honor  to  the 
sanctuary  on  the  promontory,  when  suddenly  an  earthquake  took  place.  The 
roar  of  the  thunder,  says  Philostratus,  did  not  proceed  from  the  clouds,  but 
came  from  the  depths  of  the  sea,  and  the  sea  retired  at  least  seven  stadia, 
so  that  the  crowd  were  afraid  that  in  its  retreat  it  would  carry  the  temple 
with  it,  and  wash  them  all  away.  Apollonius  however  said:  'Be  com- 
forted; the  sea  has  brought  forth  new  land!  A  few  days  later  they  heard 
that  a  new  island  had  risen  between  Thera  and  Crete." 

This  account  not  only  illustrates  the  character  of  a  philosopher, 
but  also  shows  that  even  Apollonius  recognized  that  the  sea  brought 
forth  new  land. 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  353 

§  33.  On  the  upbuilding  of  the  smaller  areas  by  gradual  upheaval. 

We  have  already  studied  the  process  of  injection  from  under  the 
bed  of  the  sea  and  have  seen  that  the  mountains  have  been  upheaved 
in  this  way. 

This  same  reasoning  is  immediately  applicable  to  narrow  islands 
like  Japan  and  Java,  with  water  on  both  sides.  Not  only  have  their 
mountains  been  thus  upraised,  and  the  volcanoes  formed  in  the  back- 
bones of  these  islands,  but  the  whole  tablelands  of  the  islands  have 
been  built  up  in  the  same  way,  by  the  gradual  injection  of  porous 
lava  from  under  the  bed  of  the  sea.  If  the  sea  was  originally  deeper 
on  one  side,  it  has  given  the  backbone  of  the  islands  a  somewhat 
unsymmetrical  form,  the  stronger  injection  and  development  coming 
from  the  deeper  sea,  but  the  uplift  sometimes  makes  a  wider  extent 
of  land  towards  the  shallower  water. 

This  is  clearly  shown  in  the  formation  of  numerous  peninsulas, 
as  Athos,  Longos,  Cassandra,  Pelion,  Attica,  Corinth,  Argolis,  and 
the  three  peninsulas  of  the  Peloponnesus  in  Greece ;  in  Italy  as  a 
whole,  and  especially  Calabria  and  Sicily,  the  latter  being  a  tri- 
angular island  with  mountains  facing  the  Tyrrhenian,  Ionian  and 
Mediterranean  Seas;  also  in  Scandinavia  and  Scotland;  in  Kamt- 
chatka,  Corea  and  the  Malay  Peninsula  of  Asia;  and  many  other 
places.  The  same  principle  is  beautifully  shown  in  such  islands  as 
Cyprus,  Crete,  Euboea  and  nearly  all  the  islands  of  the  yEgean  Sea ; 
in  numerous  islands  along  the  coast  of  Dalmatia ;  in  the  ^Eolian 
Islands,  Sardinia,  Corsica,  Elbe,  Ischia  and  the  island  of  Capri; 
Minorca,  Majorca,  Pine  Islands,  Isle  of  Wight,  and  numerous  others 
around  Scotland  and  Ireland.  Good  illustrations  in  America  are 
found  in  the  West  Indies  and  the  Catalina  Islands  off  the  Cali- 
fornia coast ;  and  in  Asia,  it  is  shown  beautifully  by  the  form  of 
Saghallien,  the  islands  of  Japan,  Formosa,  Sumatra,  Java,  and 
numerous  islands  in  the  East  Indies;  also  in  New  Zealand;  and  in 
fact  almost  universally  throughout  the  world. 

In  the  case  of  Italy,  the  Apennines  are  nearly  in  the  center  of  the 
country,  but  slightly  nearer  the  Adriatic,  which  was  the  deeper  sea, 
and  did  most  to  elevate  the  peninsula.  The  same  arrangement  is 
well  illustrated  in  the  island  of  Sicily,  where  the  highest  mountains 
face  the  deepest  seas.  All  of  these  and  many  other  obvious  illus- 


354  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

trations  of  the  principle  may  be  readily  found,  and  must  convince 
even  the  most  sceptical  of  its  general  validity. 

If  we  apply  this  principle  to  Guam,  the  Philippines,  the  Aleutian 
Islands,  Puerto  Rico  and  other  islands  of  the  Antilles,  we  shall  be 
able  to  explain  how  the  mountains  of  these  countries  have  been 
raised,  and  the  islands  themselves  developed  by  matter  injected  from 
under  the  troughs  near  them.1  This  seems  to  remove  all  doubt  as 
to  the  process  involved  in  the  formation  of  islands,  and  the  smaller 
land  areas,  and  we  may  consider  the  plains  and  slopes  of  the  larger 
land  areas  bordering  on  the  sea. 

If  the"  injections  are  powerful,  as  in  South  America,  the  up- 
heaval of  matter  by  the  power  of  steam  brings  the  subsidence  of  the 
adjacent  bottom  and  the  accompanying  sea  waves.  We  need  not 
assume,  and  we  do  not  assume,  any  original  weakness  or  line  of 
weakness  of  the  earth's  crust,  but  simply  that  the  ocean  bed  leaks, 
and  the  steam  pressure  tends  to  heave  it  up,  and  that  the  process 
works  at  various  depths  from  ten  to  twenty  miles,  and  is  continued 
at  irregular  intervals  over  long  periods. 

This  principle  of  ridges  enables  us  to  understand  why  islands 
rise  from  the  sea  in  chains — in  such  cases  they  are  really  submerged 
and  perhaps  immature  mountains.  The  Aleutian  Islands  are  now  in 
this  state,  and  many  others  may  be  pointed  out.  When  a  ridge  is 
once  started,  the  chances  greatly  favor  another  parallel  to  the  first, 
because  of  the  way  the  sea  bottom  is  depressed  nearby,  in  forcing 
up  the  islands  from  beneath. 

If  we  examine  relief  maps  of  the  world,2  we  shall  see  by  the 
mountains  parallel  to  the  shores  exactly  where  the  ocean  used  to  be 
and  how  it  gradually  withdrew.  Thus,  the  successive  ridges  of  the 

1  As  throwing  light  upon  some  remarkable  processes  of  stability  in  nature, 
it  is  interesting  to  notice  that  when  a  volcanic  cone  has  been  upheaved  in 
the  sea,  and  by  successive  uplifts  raised  above  the  water  to  become  an  island, 
the  subsidence  that  eventually  takes  place,  after  much  matter  has  been  ex- 
pelled from  beneath  the  crust  to  make  the  island,  does  not  appreciably  en- 
danger the  island  itself,  which  is  powerfully  braced  by  the  conical  form  of 
its  base.  When  a  portion  of  the  sea  bottom  sinks  near  by,  to  partially  fill  up 
the  cavities  in  the  crust,  the  settlement  of  the  bed  of  the  ocean  scarcely  dis- 
turbs the  island,  on  account  of  the  way  in  which  the  crust  is  upraised  about 
its  base,  and  braces  it  on  all  sides. 

'Those  of  Rand,  McNally  &  Co.,  given  in  the  Encyclopedia  Americana, 
have  been  found  extremely  useful. 


19o6t]  SEE— THE  CAUSE  OF  EARTHQUAKES.  355 

Andes  were  formed,  beginning  on  the  east,  and  working  westward ; 
as  the  movement  progressed  the  chains  got  higher  and  higher, 
requiring  increased  volcanic  forces ;  and  in  the  last  range,  therefore, 
occur  the  most  and  the  highest  volcanoes.  This  principle  seems  to 
hold  not  only  in  the  Andes,  but  generally  throughout  the  world. 

§  34.  On  the  formation  of  islands,  and  on  the  significance  of  the 
symmetrical  disposition  of  their  mountains. 

We  have  already  explained  the  formation  of  mountains  and  have 
seen  that  they  are  not  due  to  any  shrinkage  of  the  globe  with  result- 
ing collapse  of  the  crust,  but  to  the  injection  of  lava  from  the  sea, 
which  uplifts  the  crust  into  a  parallel  ridge.  The  subject  of  island 
formation,  already  alluded  to  in  §  33,  has  not  been  much  discussed, 
and  it  is  impossible  to  say  that  there  is  any  recognized  theory  on  the 
subject.  When  the  islands  are  small  they  are  justly  considered 
mountains  in  the  sea.  Some  islands  are  volcanic  and  are  thus  vol- 
canoes pushed  up  in  the  sea  like  those  occasionally  raised  on  the 
land.  That  volcanic  islands  are  similar  to  ordinary  land  volcanoes 
seems  clear  enough ;  but  how  about  the  larger  islands  ?  How  did 
they  originate?  To  answer  this  question  satisfactorily,  we  may 
remark  that  when  we  look  at  an  ocean  like  the  Pacific  and  notice 
how  it  is  dotted  all  over  with  peaks  projecting  above  the  water,  and 
remember  that  a  still  greater  number  do  not  reach  the  surface,  we 
recognize  that  such  peaks  were  no  part  of  the  original  constitution 
of  the  globe,  but  have  been  developed  in  the  sea  in  the  course  of 
immeasurable  ages. 

Now,  as  to  the  larger  islands,  many  of  them  have  conspicuous 
mountain  chains,  and  the  study  of  the  lay  of  these  chains  is  very 
instructive.  If  mountains  are  wrinkles  in  the  earth's  crust,  due  to 
the  shrinkage  of  the  globe,  there  is  certainly  no  reason  why  they 
should  be  symmetrically  placed  on  islands.  On  this  theory,  the 
mountains  might  cross  the  islands  at  any  angle,  or  even  miss  the 
islands  entirely.  On  actual  examination,  what  do  we  find  to  be  the 
fact?  When  we  look  at  any  good  map  we  see  the  mountains  run- 
ning through  the  islands  with  the  utmost  symmetry,  making  in  all 
cases  a  veritable  backbone  or  central  axis  for  the  land  on  both  sides 
In  no  cases  do  the  mountains  run  diagonally  or  crosswise.  To 
appreciate  the  significance  of  this  arrangement,  look  at  the  map  of 


356  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

such  islands  as  Cyprus,  Crete,  and  others  in  the  Mediterranean, 
Saghallien,  Formosa,  Sumatra,  Java,  and  others  in  the  East  Indies. 
The  regular  symmetry  of  the  mountains  makes  them  in  all  cases  the 
backbones  of  the  islands,  and  this  can  only  mean  that  they  were 
formed  in  their  present  position  by  injections  from  the  ocean  on 
both  sides ;  in  no  other  way  could  such  a  symmetrical  arrangement 
arise.  The  universality  of  this  law  shows  that  the  mountains  depend 
on  the  sea,  and  not  at  all  on  the  shrinkage  of  the  globe.  The  same 
symmetrical  arrangement  is  shown  in  numerous  peninsulas  through- 
out the  world. 

§  35-  Why  all  upheavals  do  not  produce  volcanoes. 

It  is  not  necessary  for  the  subterranean  forces  to  break  through 
and  form  volcanoes — the  movement  often  becomes  so  deep-seated 
or  feeble  with  the  raising  of  the  mountains  that  outbreaks  do  not 
occur.  What  takes  place  in  this  respect  depends  on  the  depth  and 
recession  of  the  sea  and  the  suddenness  and  violence  with  which  the 
upheaving  pressure  is  exerted.  Thus,  along  the  east  coast  of  South 
America  no  large  volcanoes  were  formed,  and  such  small  ones  as 
may  have  once  existed  have  now  lost  all  trace  of  a  volcanic  aspect, 
because  the  sea  was  shallow  and  kept  retreating.  On  the  northeast 
of  South  America,  however,  the  Lesser  Antilles  are  in  deeper  water, 
and  when  they  rise  to  full  growth  may  form  a  somewhat  imposing 
chain  of  mountains,  exhibiting  volcanic  violence  depending  on  the 
depth  of  the  sea. 

In  the  case  of  the  Alps  the  development  was  arrested  by  the  rise 
of  Italy  from  the  Mediterranean,  which  stopped  the  sinking  of  the 
deep  trough  which  has  since  become  Lombardy.  This  was  formerly 
the  Alpine  trough,  and  it  is  now  so  filled  up  by  erosion  that  the 
Adriatic  is  the  nearest  sea,  the  recognized  recession  of  which  con- 
firms the  law. 

In  the  case  of  the  Himalayas  also  the  development  was  arrested 
by  the  rise  of  the  vast  plain  of  India.  And  while  the  resulting  moun- 
tain range  became  high,  volcanic  force  was  at  length  enfeebled  by 
the  shallowness  of  the  troughs  where  the  Indus  and  the  Ganges  now 
flow,  and  thus  it  is  supposed  that  no  active  volcanoes  broke  forth 
on  the  tops  of  these  mighty  mountains.  If  the  adjacent  water  had 
remained  deep,  as  off  the  west  coast  of  South  America,  the  Hima- 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  357 


lavas  would  doubtless  have  been  broken  through  by  the  resulting 
violence  of  the  volcanic  forces.  As  it  was  the  shallow  water, 
eventually  supervening,  gave  the  power  for  heaving  the  mountains 
little  by  little,  and  when  they  attained  great  height  became  so  feeble 
or  deep-seated  that  it  left  them  unbroken  by  volcanic  violence.  Thus 
we  see  why  the  Alps  and  the  Himalayas,  in  the  main,  failed  to  form 
volcanoes,  and  why  Africa  and  Australia  are  also  devoid  of  these 
vents  (many  small  ones  may  have  existed  and  have  since  lost  all 
trace  of  this  appearance),  which  chiefly  develop  near  the  deep  sea, 
where  the  sudden  exertion  of  these  forces  break  through  the  moun- 
tain tops.  This  happens  in  some  cases  where  the  mountains  are  not 
very  high,  either  because  the  seat  of  the  explosion  is  shallow  or  the 
fractures  such  as  to  offer  but  little  resistance  from  greater  depth. 

In  order  to  break  through  high  mountains,  the  force  has  to  be 
extremely  powerful,  and  this  is  not  likely  to  be  the  case  where  the 
adjacent  sea  is  shallow,  as  was  true  south  of  the  Alps  and  the 
Himalayas. 

Earthquakes  in  these  regions,  however,  still  continue,  and  have 
always  been  abundant,  but  they  are  deep-seated,  owing  largely  to 
the  filling  in  of  the  Alpine  and  Himalayan  troughs,  and  lead  to  no 
eruptions,  and  hence  have  been  called  tectonic.  They  are  clearly  a 
survival,  due  to  the  same  forces  which  upheaved  the  mountains,  but 
the  sea  having  so  far  receded  they  cannot  blow  open  any  cones  at 
this  late  date.  In  fact  the  centers  of  disturbances  usually  are  some- 
what remote  from  the  mountains  at  present  and  diffused  over  such 
an  area  in  the  ancient  trough  that  their  power  for  rupture  is  slight. 

§  36.  Gradual  secular  desiccation  of  the  oceans  indicated  by  the 
lowering  of  the  strand  lines  throughout  the  world. 

The  raising  and  lowering  of  the  land  by  subterranean  forces 
which  have  effected  the  withdrawal  and  encroachment  of  the  sea  over 
the  land  was  first  advocated  by  the  Greek  geographer  Strabo,  who 
adopted  the  theory  of  Archimedes  that  the  figure  of  the  ocean  sur- 
face is  that  of  a  sphere  (cf.  Suess,  "  Face  of  the  Earth,"  Vol.  II, 
p.  2).  This  theory  has  been  much  developed  in  modern  times  and 
explains  numerous  movements  of  the  strand  line.  But  according 
to  the  elaborate  study  of  this  question  made  by  Professor  Suess,  the 
elevation  and  subsidence  theory  even  in  the  oscillatory  form  adopted 


358  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  i9, 

by  Lyell,  is  inadequate  to  account  for  the  general  lowering  of  the 
strand  line  noticed  throughout  the  world.  After  his  careful  study 
of  this  question,  Professor  Suess  is  unable  to  adopt  any  satisfactory 
explanation  of  the  observed  phenomenon,  and  the  whole  problem 
remains  an  enigma  to  the  investigator  of  the  physics  of  the  earth. 
An  impartial  examination  of  all  the  arguments  leads  me  to  believe 
that  the  conceptions  of  Strabo,  as  developed  into  the  oscillatory  theory 
advocated  by  Lyell,  is  adequate  to  account  for  many  more  of  the 
phenomena  of  the  earth's  surface  than  Professor  Suess  concedes; 
yet  it  seems  not  only  possible,  but  even  probable,  that  an  additional 
cause  is  at  work  which  must  contribute  somewhat  to  the  general 
lowering  of  the  strand  line  throughout  the  world.  This  additional 
cause  is  nothing  else  than  the  secular  desiccation  of  the  oceans, 
brought  about  mainly  by  the  sinking  of  the  waters  into  the  crust  of 
the  earth,  where  the  resulting  steam  becomes  the  motive  power  in 
earthquakes.1  A  certain  amount  of  water  is  also  taken  up  as  water 
of  crystallization  in  the  development  of  crystalline  rocks,  which 
extend  somewhat  deeper  from  age  to  age. 

The  view  of  earthquakes  here  adopted  makes  sea  water  the  prin- 
cipal disturbing  cause.  Of  the  water  which  thus  sinks  below  the 
crust,  an  appreciable  part,  but  by  no  means  all  of  it  is  expelled  by 
volcanic  action ;  and  thus  there  is  a  steady  accumulation  of  water 
deep  down  in  the  earth's  crust.  If  this  view  be  well  founded,  there 
is  thus  a  secular  desiccation  of  the  waters  of  the  globe,  depending 
on  the  penetration  of  water  to  the  deeper  parts  of  the  crust,  and  also 
on  the  absorption  of  water  by  rocks  in  crystallization  and  otherwise. 
How  rapidly  this  process  goes  on  cannot  be  accurately  known  at 
present;  but  on  the  basis  of  data  observed  within  the  historical 
period,  we  may  reasonably  hold  that  the  fall  of  the  strand  line  due 
to  this  cause  is  on  the  average  less  than  a  meter  in  2,000  years,  and 
most  likely  of  the  order  of  one-tenth  of  this  amount. 

The  desiccation  here  postulated  seems  to  be  a  vera  causa,  and 
this  process,  in  connection  with  the  oscillatory  movement  of  the 
land  recognized  by  Lyell  and  other  geologists  as  necessary  for  the 

1  The  sinking  of  the  sea  bottom  when  lava  is  expelled  from  under  it  also 
increases  the  capacity  of  the  ocean  basins,  and  thus  slightly  lowers  the  strand 
line. 


xgo6]  SEE— THE  CAUSE  OF  EARTHQUAKES.  359 

explanation  of  such  phenomena  as  the  coal  measures,  gives  us  a 
simple  and  natural  way  of  explaining  leading  phenomena  of  the 
strand.  We  have  elsewhere  explained  why  the  movements  of  faults 
must  be  attributed  primarily  to  the  formation  of  steam-saturated 
lava  at  the  depths  whence  earthquakes  originate. 

The  steam  which  induces  this  movement  naturally  remains  hidden 
in  the  earth,  and  as  the  process  goes  on  uninterruptedly  from  one 
geological  age  to  another,  there  is  a  gradual  secular  desiccation  of 
the  waters  of  the  sea,  and  a  correspondingly  slow  lowering  of  the 
strand  line. 

To  determine  the  average  rate  of  this  lowering  of  the  strand  we 
would  have  to  take  a  figure  somewhat  smaller  than  that  found  in  the 
different  countries  since  a  given  geological  epoch,  and  even  then, 
the  result  would  be  partly  vitiated  by  the  effects  of  secular  elevation 
of  the  land.  In  any  case,  the  movement  depending  on  secular  desic- 
cation of  the  oceans  is  extremely  slow. 

This  view  that  there  is  a  secular  desiccation  of  the  waters  of  the 
sea  is  not  new,  but  was  entertained  in  different  forms  by  Benoist  de 
Maillet  (1692),  Celsius  (1743),  Von  Hoff  (1822),  Goethe  and 
others  (cf.  Suess,  "  Face  of  the  Earth,"  Vol.  II,  Ch.  I). 

Professor  Suess'  exhaustive  discussion  of  the  movements  of  the 
strand  line  will  be  found  chiefly  in  chapters  XII-XIV  of  Volume 
II  of  the  "  Face  of  the  Earth."  He  considers  the  lowering  of  the 
sea  level  to  the  extent  of  hundreds  of  meters  within  recent  geo- 
logical time  to  be  proved.  The  cause  here  suggested  gives  the  only 
explanation  of  the  phenomenon  which  seems  at  all  probable  or 
consistent  with  known  facts. 

§  37.  On  the  gentle  movements  of  the  land. 

In  many  parts  of  the  world,  the  rocks  are  comparatively  un- 
broken, and  leakage  is  very  slow  and  gradual.  This  may  corre- 
spond to  the  beds  of  shallow  seas  or  to  the  land  when  level  and 
unbroken  by  mountains.  In  all  such  regions  the  water  which  may 
seep  down  would  give  rise  to  a  very  evenly  diffused  subterranean 
steam  pressure  and  the  chances  are  that  any  movement  which  might 
take  place  would  prove  to  be  very  slow  and  gradual.  The  strain 
being  nearly  equalized  at  all  points,  there  would  be  no  heaving  re- 
quired to  adjust  the  nearly  even  balance  of  the  forces,  and  conse- 

PROC.  AMER.   PHIL.  SOC.,  XLV.    184  W,  PRINTED  FEBRUARY  2J,   1907. 


360  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

quently  earthquakes  of  sensible  strength  would  seldom  or  never 
occur.  In  this  way  we  may  explain  the  comparative  immunity  of 
many  districts  from  earthquakes. 

Yet,  when  an  even  pressure  thus  arises,  it  may  produce  a  steady 
elevation  of  the  land.  Bending  and  warping  of  the  strata  may  also 
occur  where  the  stresses  are  steadily  applied,  and  under  the  cir- 
cumstances the  rocks  would  probably  change  their  figure  slowly 
without  snapping;  when  the  earthquakes  are  more  violent  the  rocks, 
are  broken  into  smaller  pieces  and  fault  movements  increase. 

§  38.  Oscillations  of  the  strand  shown  in  such  phenomena  as  the 
coal  measures  and  fossil  beds. 

No  special  effort  is  made  in  this  paper  to  explain  all  the  phe- 
nomena of  the  earth's  crust  which  offer  difficulty  to  the  geologist; 
and  hence  we  have  been  chiefly  concerned  with  phenomena  of  eleva- 
tion. But  ever  since  the^time  of  Aristotle  and  Strabo  it  has  been 
justly  remarked  by  sagacious  observers  that  there  has  been  not 
only  elevation  of  the  land,  but  under  certain  conditions  also  subsi- 
dence. Lyell  and  many  other  writers  have  discussed  these  oscillatory 
movements  which  are  well  exhibited  by  the  successive  layers  seen 
in  many  of  the  coal  measures.  Some  of  these  layers  may  be  ex- 
plained by  the  effects  of  damming  up  and  drifting  of  vegetation  to 
places  where  it  did  not  grow ;  but  even  when  allowance  is  made  for 
these  causes,  there  still  seems  ample  evidence  of  an  oscillatory  move- 
ment of  the  land  in  many  places.  This  is  also  well  shown  in  fossil 
beds,  where  sea  shells  often  alternate  with  brackish  water  species. 

The  expansion  and  contraction  of  the  limits  of  the  sea  over  large 
areas  of  the  low-lying  shore  is  a  frequent  phenomenon,  and  a  slow 
oscillation  of  the  strand  seems  the  only  rational  explanation  of  it  yet 
offered.  Such  an  oscillation  is  most  easily  explained  by  a  sub- 
stratum of  fluid  beneath  the  earth's  crust,  such  as  we  show  to  exist. 
Under  just  what  conditions  the  land  sinks  is  not  clear.  The  insta- 
bility may  result  from  a  number  of  causes  of  which  the  most  probable 
would  seem  to  be:  upward  movement  of  neighboring  regions,  thus 
weakening  the  support  of  the  region  in  question  and  perhaps  putting 
additional  load  upon  it,  while  the  underlying  fluid  layer  slowly 
yields,  thus  causing  subsidence.  If  during  an  earthquake  a  neigh- 
boring area  should  be  started  upward,  the  strain  would  naturally 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  361 

equalize  itself  in  that  direction,  and  the  movement  might  continue 
for  a  long  time  until  subterranean  conditions  changed.  The  earth's 
crust  is  complex,  of  unequal  thickness  in  different  parts,  and  broken 
into  unequal  blocks  by  various  faults,  which  are  continually  adjust- 
ing themselves  to  the  strains  arising  in  the  underlying  substratum 
supporting  them.  That  some  areas  should  go  up  while  others  go 
down  is  therefore  not  at  all  remarkable ;  and  most  of  the  oscillations 
of  the  land  will  be  found  to  depend  upon  causes  of  this  kind.  In 
my  opinion  the  seat  of  the  forces  will  be  found  to  lie  mainly  in  the 
fluid  substratum  beneath.  Considering  the  great  number  of  blocks 
into  which  the  earth's  crust  has  been  shown  to  be  broken  by  faults 
such  as  Professor  Suess  has  so  fully  discussed  for  the  regions  of 
the  Alps  and  the  Tyrol,  the  oscillations  of  level  with  the  changes  of 
the  strand  in  salt  and  fresh  water  regions  seem  easily  accounted  for. 
In  his  work  on  "  Meteorics "  (lib.  I,  cap.  12)  Aristotle  justly 
remarks : 

"  The  distribution  of  land  and  sea  in  particular  regions  does  not  endure 
throughout  all  time,  but  it  becomes  sea  in  those  parts  where  it  was  land, 
and  again  it  becomes  land  where  it  was  sea.  .  .  . 

"  And  the  sea  also  continually  deserts  some  lands  and  invades  others. 
The  same  tracts,  therefore,  of  the  Earth  are  not,  some  always  sea,  and  others 
always  continents,  but  everything  changes  in  the  course  of  time."  1 

§  39.  Strabo's  vieivs  on  the  elevation  and  depression  of  the  land. 

In  his  "  Principles  of  Geology  "  (pp.  24-25,  I2th  edition)  Lyell 
quotes  the  views  of  Strabo  regarding  the  elevation  and  depression 
of  the  land  as  follows : 

"  It  is  not,"  says  Strabo,  "  because  the  lands  covered  by  seas  were  orig- 
inally at  different  altitudes,  that  the  waters  have  risen,  or  subsided,  or  receded 
from  some  parts  and  inundated  others.  But  the  reason  is,  that  the  same 
land  is  sometimes  raised  up  and  sometimes  depressed,  and  the  sea  also  is 
simultaneously  raised  and  depressed,  so  that  it  either:  overflows  or  returns 
into  its  own  place  again.  We  must,  therefore,  ascribe  the  cause  to  the 
ground,  either  to  that  ground  which  is  under  the  sea,  or  to  that  which  be- 
comes flooded  by  it,  but  rather  to  that  which  lies  beneath  the  sea,  for  this 
is  more  movable  and,  on  account  of  its  humidity,  can  be  altered  with  great 
celerity.  It  is  proper  to  derive  our  explanations  from  things  which  are 
obvious,  and  in  some  measure  of  daily  occurrence,  such  as  deluges,  earth- 
quakes and  volcanic  eruptions,  and  sudden  swellings  of  the  land  beneath  the 
,  sea ;  for  the  last  raise  up  the  sea  also ;  and  when  the  land  subsides  again,  they 
occasion  the  sea  to  be  let  down.  And  it  is  not  merely  the  small,  but  the 

1  Cf.  Lyell's  "  Principles  of  Geology}"  I2th  edition,  Vol.  I,  pp.  21-22. 


362  SEE -THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

large  islands  also,  and  not  merely  the  islands,  but  the  continents  which  can 
be  lifted  up  together  with  the  sea ;  and  both  large  and  small  tracts  may  sub- 
side, .  for  habitations  and  cities,  like  Bure,  Bizona,  and  many  others,  have 
been  engulfed  by  earthquakes." 

VIII.     ON  THE  GREAT  SEA  WAVES  WHICH  FREQUENTLY  ACCOMPANY 
VIOLENT  EARTHQUAKES. 

§  40.  Great  sea  zvaves  caused  chiefly  by  the  subsidence  of  the  sea 
bottom  after  the  lava  has  been  expelled  by  the  throes  of  earthquakes. 

We  have  already  shown  how  the  sea  bottom  may  subside  over  a 
large  area  after  a  violent  earthquake  which  has  forced  out  from  be- 
neath the  bed  a  large  amount  of  steam-saturated  lava.  This  lava 
is  usually  forced  up  under  adjacent  mountain  ranges,  mountain 
peaks  and  volcanoes,  or  under  the  intervening  coast  plains.  If 
relief  is  afforded  by  forcing  the  column  of  molten  matter  along  so 
that  the  remotest  part  raises  in  the  mountains,  which  are  at  the  top 
of  the  arched  portion  of  the  neighboring  region  of  crust,  we  should 
have  no  means  of  discovering  the  resulting  slight  elevation  of  the 
peaks.  For  the  heights  of  mountains  are  always  uncertain  by  several 
feet,  because  extremely  exact  levels  are  difficult  to  establish  so  far 
above  the  sea.  We  are  thus  unable  to  say  whether  the  various 
peaks  and  ranges  are  rising  in  height,  or  to  tell  what  fluctuation  of 
altitude  they  may  undergo  from  time  to  time,  by  the  heaving  of 
earthquakes.  In  the  case  of  plains  near  the  sea  it  is  easier  to  detect 
changes  of  level,  but  in  many  places  characterized  by  violent  earth- 
quakes unfortunately  no  such  observations  are  taken.  Tidal  obser- 
vatories are  best  adapted  to  keeping  record  of  any  changes  of  level 
that  may  occur,  because  it  is  only  by  analyzing  the  tides  carefully 
that  we  can  detect  changes  of  the  sea  level. 

As  already  remarked,  the  sudden  upheaval  noticed  in  the  sea- 
coast  of  Chili  after  certain  earthquakes  was  especially  remarked  by 
Charles  Darwin  and  Capt.  Fitzroy,  who  experienced  the  severe 
earthquake  at  Conception,  February  20,  1835,  and  noticed  the  result- 
ing elevations  of  the  coast  line. 

Let  us  consider  briefly  the  upheavals  of  the  Chilian  coast  wit- 
nessed by  Darwin  and  Fitzroy.  The  only  reasonable  explanation 
of  this  fact  is  that  lava  had  been  forced  under  the  coast,  and  it  is 
obvious  that  the  matter  must  have  been  expelled  from  under  the 


i9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  363 

bed  of  the  sea.  We  do  not  know  whether  the  lava  was  injected  as 
a  thin  layer  or  the  whole  body  of  the  material  under  the  coast  slightly 
pushed  back  to  afford  relief  of  the  strain  under  the  sea,  but  a  dis- 
placement of  the  latter  kind  seems  the  more  probable.  A  sea  wave 
of  considerable  magnitude1  was  noticed  on  that  occasion,  but  it  was 
not  so  large  as  sometimes  develops,  and  the  sea  bottom  may  have 
subsided  only  very  slightly.  But  on  August  13,  1868,  the  whole 
South  American  coast  from  Valdivia  in  Chili  to  Guayaquil  in  Ecua-' 
dor  was  violently  shaken  by  a  terrible  earthquake,  with  its  highest 
intensity  near  Arica.  A  few  minutes  after  the  earthquake  the  ob- 
servers were  surprised  and  alarmed  to  notice  the  sea  slowly  receding 
from  the  land,  and  very  soon  vessels  which  had  been  anchored  in 
seven  fathoms  of  water  were  left  high  and  dry,  with  no  means  <5f 
escape.  In  a  short  time  their  surprise  was  converted  into  terror  at 
the  sight  of  a  mighty  ocean  wave  fifty  or  sixty  feet  high  returning 
with  terrible  velocity  and  carrying  everything  before  it.  The  vessels 
stranded  on  the  beach  at  Arica,  including  the  U.  S.  S.  Wateree, 
were  swept  up  by  the  gigantic  wave  and  carried  nearly  a.  half  mile 
inland  and  again  left  stranded  higher  than  before.2  The  wave  rolled 
back  and  after  a  short  interval  again  swept  the  shore ;  and  the 
furious  oscillation  of  the  water  thus  started  continued  for  a  day 
or  two  before  the  sea  finally  quieted  down.  This  great  sea  wave  was 
propagated  over  the  Pacific  and  observed  almost  all  over  the  world. 
In  1877,  May  9,  another  great  earthquake  visited  the  same 
region  and  was  followed  by  a  wave  of  even  greater  magnitude,  of 
exactly  the  same  type,  the  water  first  slowly  receding  from  the  land, 
and  then  returning  as  a  gigantic  wave  carrying  everything  before  it. 
This  wave  of  1877  is  known  as  the  Iquique  wave.  At  Arica  the 
hulk  of  the  stranded  U.  S.  S.  Wateree  was  again  picked  up  and 
carried  still  furthe'r  inland,  which  would  indicate  that  at  Arica  the 
height  of  this  wave  surpassed  that  of  1868.  The  sea  continued  to 
oscillate  in  periods  of  something  like  an  hour  and  did  not  subside 
for  a  couple  of  days. 

1  In  his  valuable  work  on  "  Earthquakes,"  chapter  IX,   Professor  Milne 
gives  a  catalogue  of  sea  waves.     Different  waves  present  different  phenomena, 
and  we  here  treat  only  of  the  best  established  types. 

2  Button,  "  Earthquakes  in  the  Light  of  the  New  Seismology,"  p.  281. 


364  SEE—  THE  CAUSE  OF  EARTHQUAKES.  [October  i9, 

These  two  are  good  types  of  those  great  sea  waves  in  which  the 
water  recedes  from  the  land  in  the  first  few  minutes  following  the 
earthquake. 

Major  Button  and  others  have  suggested  that  the  sea  bottom 
sinks,  and  the  explanation  we  have  given  of  how  this  takes  place 
seems  satisfactory  and  free  from  objections.  It  is  clear  that  if  by 
the  throes  of  the  earthquake  a  large  body  of  lava  is  forced  from 
under  the  bed  of  the  Andean  trough,  the  bed  might  thereupon  settle 
from  twenty  to  fifty  feet  over  a  large  area.1  The  great  inrush  of 
the  water  following  this  subsidence  would  withdraw  it  from  the  land, 
and  as  soon  as  the  rushing  currents  met  in  the  center  of  the  trough, 
they  would  raise  the  water  into  a  high  ridge,  and  its  subsidence  would 
give  the  first  great  wave  which  rolled  in  upon  the  devastated  shore. 
With  the  first  depression  of  the  water  over  the  ridge,  another  in- 
rush would  take  place,  again  withdrawing  the  sea  from  the  shore, 
and  another  great  wave  would  follow  like  the  first,  but  of  slightly 
feebler  intensity.  And  so  the  oscillations  of  the  sea  would  con- 
tinue for  a  day  or  two,  till  they  became  reduced  by  friction  to  in- 
sensible magnitude.  This  explanation  accords  with  all  the  known 
facts,  and  the  recognized  laws  of  fluid  motion.  Assuming  it  to  be 
^correct,  the  result  is  of  interest  as  showing  the  effect  of  friction  in 
destroying  the  motion  of  the  sea,  which  has  often  been  discussed  in 
connection  with  the  problem  of  the  tides.  In  this  case,  the  length  of 
the  wave  of  1868  has  been  calculated  to  be  about  100  geographical 
miles  ;  and  as  the  depth  of  the  sea  is  between  four  and  five  miles,  we 
see  that  the  wave  length  involved  is  from  twenty  to  twenty-five  times 
the  depth  of  the  sea. 

At  the  close  of  this  section  we  shall  give  another  possible  ex- 
planation of  waves  of  this  kind,  which  begins  with  a  recession  of 
the  water  from  the  shore  ;  but  meanwhile  we  shall  notice  waves  of 
a  different  class,  sometimes  encountered,  which  begin  by  a  sudden 
rising  of  the  water  near  shore. 

The  great  wave  which  overwhelmed  Simoda,  Japan,  December 
29,  1854,  may  be  taken  as  a  type  of  those  which  are  characterized 
by  the  sudden  inrush  of  a  great  wave  without  any  previous  recession 


subsidence  might  be  much  greater  if  the  area  affected  was  propor- 
tionally diminished. 


tgob.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  365 


of  the  sea  near  the  shore.  At  9:15  a.  m.  Vice  Admiral  Putiatin  on 
board  the  Russian  frigate  Diana  noted  very  powerful  shocks  of  an 
earthquake,  and  a  little  before  ten  o'clock  a  huge  wave  was  seen 
coming  which  quickly  overflowed  the  city.  Major  Button  remarks 
that  the  time  here  involved,  and  the  known  speed  of  propagation  of 
such  a  wave,  indicates  that  it  originated  over  100  miles  from  the 
shore,  in  the  Tuscarora  trough,  where  the  depth  attained  is  over 
4,000  fathoms. 

If  it  originated  so  far  away,  it  might  have  resulted  from  the 
sinking  of  the  sea  bottom,  as  in  the  Arica  and  Iquique  waves,  the 
withdrawal  of  the  sea  when  the  waters  rush  into  the  sink  becoming 
so  nearly  insensible  at  the  great  distance  of  Simoda  as  to  escape 
notice  in  the  bay.  But  a  more  probable  explanation  is  that  the  sea 
bottom  just  east  of  the  Tuscarora  deep  was  heaved  up  into  a  ridge 
with  elevation  of  20,  30,  or  50  feet.  This  would  produce  the 
great  wave  which  so  suddenly  appeared  to  overwhelm  the  city. 
In  this  case  there  would  be  no  preliminary  recession  of  the  water 
whatever,  and  the  wave  would  come  without  the  least  warning,  as 
appears  to  have  been  the  case. 

In  case  the  wave  originated  by  a  subsidence  of  the  bottom  of 
that  trough,  a  slight  withdrawal  of  the  water  from  shore  should 
have  been  noticed  even  at  that  great  distance;  but  if  the  upheaval 
occurred  beyond  the  trough,  the  greater  inrush  of  water  from  that 
side  may  have  obscured  the  slight  recession  which  otherwise  might  be 
expected  at  Simoda.  The  upheaval  is  conceivable  in  the  manner 
we  have  described,  either  with  or  without  subsidence  of  the  bed, 
and  ordinarily  the  disturbance  might  be  on  either  side  of  the 
trough ;  but  in  this  case  the  time  shows  that  the  uplift  probably  was 
beyond  the  trough. 

§41.  Another  explanation  of  sea  waves  on  the  hypothesis  of 
submarine  eruptions. 

The  only  other  rational  way  of  explaining  these  great  sea  waves 
is  by  means  of  the  uprush  following  the  explosion  of  a  submarine 
volcano.  We  consider  his  explanation  much  less  satisfactory  than 
that  already  given,  but  it  is  undeniable  that  in  certain  cases  it  might 
account  for  both  classes  of  sea  waves,  especially  where  the  water  is 
deep  and  we  can  suppose  the  volcano  to  be  upheaved  near  shore  and 
of  large  size. 


366  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

Let  the  accompanying  figure  illustrate  a  section  perpendicular 
to  the  shore  of  the  sea  and  land,  on  a  coast  like  that  of  Chili  or  Peru, 
where  this  phenomenon  has  so  often  been  observed  in  a  typical  way, 
and  the  water  is  deep. 

Suppose  a  volcano  to  be  formed  at  some  distance,  say  50  or  100 
kilometers  from  the  shore.  If  a  great  wave  is  produced  we  may 
assume  the  volcano  to  be  raised  to  a  height  of  1,000  or  2,000  meters, 
or  even  higher ;  but  as  the  sea  is  seven  or  eight  kilometers  deep,  this 
will  only  reach  one-seventh  or,  at  most,  one-fourth  of  the  way  to  the 
surface.  In  the  throes  of  the  earthquake  the  volcano  is  raised,  and 
the  water  forced  up  immediately  over  the  eruptive  center;  and  the 
steam,  stones,  lava,  dust  and  ashes  are  driven  upward  towards  the 
surface,  as  in  the  explosion  of  a  land  volcano.  The  explosion  is 

FIG.  14. 


Submarine  volcano. 

resisted  by  the  great  depth  of  the  water,  which  is  hurled  upward  in 
a  violent  current  from  the  orifice.  The  steam  condenses  to  water 
by  the  low  temperature  of  the  ocean,  and  the  other  gases  are  ab- 
sorbed, whether  coming  from  the  bed  of  the  sea  or  formed  in  the 
water  by  the  intense  heat  of  the  red  hot  lava.  The  current  of  steam 
and  flying  stones,  lava,  sand  and  ashes,  by  beating  against  the  over- 
lying stratum  of  water,  forces  such  rapid  upward  movement  that  the 
level  above  is  forced  bodily  upward,  it  may  be  several  hundred 
meters.  But  the  fluid  medium  is  continuous  and  presses  in  on  all 
sides,  and  is  therefore  drawn  upward  on  all  sides  about  the  base  of 
the  cone  to  supply  the  uprush  of  water.  The  currents  thus  forced 
with  enormous  violence  are  shown  in  the  figure.  The  drawing 
upward  of  the  water  about  the  base  of  the  cone  causes  the  inflow 
of  water  from  the  bed  of  the  sea  towards  the  base  to  maintain  the 
upward  movement,  following  the  upheaval  and  explosion  of  the 
volcano.  Thus  the  water  near  the  shore  some  distance  away  is 
sucked  down  in  the  general  lowering  of  the  level  and  the  sea  is 
observed  to  slowly  recede  at  the  shore.  All  this  is  done  in  a  short 


19o6.]  SEE-THE  CAUSE  OF  EARTHQUAKES.  367 

time,  say  30  minutes,  and  then  follows  the  sea  wave  which  has  taken 
form  owing  to  the  forcing  up  of  the  water  over  the  volcano,  thus 
forming  the  crest,  and  its  withdrawal  from  the  shore,  forming  the 
trough. 

The  water  heaved  up  gradually  settles  and  the  wave  approaches 
the  shore  often  with  a  velocity  of  something  like  eight  kms.  per 
minute  and  thus  sweeps  everything  before  it.  It  then  oscillates 
back  and  forth  with  period  of  some  60  minutes,  and  for  a  day  or  two 
the  sea  may  continue  to  be  agitated  with  appalling  violence,  and  the 
wave  propagated  to  the  remotest  parts  of  the  earth. 

If  an  observer  were  to  witness  such  an  earthquake  in  a  region 
where  the  shore  was  steep  and  the  sea  of  uniform  depth,  and  should 
note  the  time  of  the  sea  wave  and  the  direction  of  the  normal  to 
the  wave  front  as  it  first  returns,  he  would  have  a  very  approximate 
means  of  locating  the  situation  of  the  new  submarine  volcano.  It 
would  lie  on  the  normal  to  the  circular  wrave  front,  and  at  a  distance 
corresponding  to  the  time  of  arrival  in  a  sea  of  the  given  depth. 

The  interval  r  required  for  the  oscillation  of  the  wave  being 
known,  the  theory  of  the  wave  motion  could  be  worked  out  by  the 
general  formula1  for  a  wave  of  any  length  A  and  any  depth  of  the 
water  k, 


^—  -^T~  (I) 

£*-   I 

Perhaps  it  could  be  found  with  sufficient  approximation  by  the  more 
special  forms,  in  which  the  velocity  becomes,  when  the  wave  is  long 
compared  to  depth  of  the  water: 


V=  Vgk,  or  V=  (k  +  E)  (2k  +  E) ;  (2)' 

E  being  the  height  of  the  crest  of  the  wave  above  the  normal  level 
of  the  water. 

In  this  way  we  could  find  not  only  the  distance  of  the  eruption 
from  the  observer,  but  the  direction,  so  as  to  fix  its  place  with  con- 

1  Airy,  "  Tides  and  Waves,"  Art.  169. 

2  Report  of  Committee  of  the  Royal  Society  on  the  Krakatoa  Eruption, 
p.  94. 


368  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

siderable  accuracy.  If  the  depth  is  not  uniform,  but  the  topography 
of  the  ocean  basin  known,  the  observer  would  still  be  able  to  locate 
the  hypothetical  submarine  volcano  with  considerable  precision.1 

Within  historical  times  several  submarine  volcanoes  have  been 
observed  to  rise  above  the  sea  about  South  America  and  elsewhere, 
in  places  where  the  depth  was  small.  From  the  circumstances  that 
the  sea  is  generally  very  deep  off  the  Chilian  and  Peruvian  coast, 
where  the  most  violent  earthquakes  occur,  one  would  expect  but 
very  few  of  these  volcanoes  to  reach  the  surface.  Yet  the  large 
number  of  sea  waves  following  violent  earthquakes  may  afford  us 
some  idea  of  the  activity  of  submarine  earthquakes  and  perhaps 
volcanoes  in  that  part  of  the  world.  It  is  probable  that  not  less 
than  one  hundred  such  earthquakes  with  sea  waves  occur  along  the 
South  American  coast  in  a  century,  and  of  these  not  less  than  ten 
have  done  great  damage. 

If  the  supposed  eruption  is  some  distance  out  at  sea,  the  effect 
on  shore  would  be  small,  because  the  level  is  not  so  much  changed, 
owing  to  the  great  body  of  the  intervening  water.  Also,  when  a 
violent  earthquake  occurs  and  but  slight  recession  of  the  water  is 
noted,  followed  by  a  wave  after  considerable  interval,  the  indications 
would  point  to  a  great  eruption  at  considerable  distance.  On  the  other 
hand,  if  the  recession  of  the  water  is  quick  and  the  wave  returns 
after  a  short  interval,  the  eruption  should  be  comparatively  near  the 
shore.  Thus  by  a  study  of  the  waves  observed  the  place  and  char- 
acter of  the  eruption  may  be  approximately  determined. 

In  some  cases  the  sea  is  said  to  be  bodily  upheaved,  and  rises 
with  the  utmost  suddenness.  In  such  cases  the  volcano  may  be 
very  near  shore,  or  the  sea  bottom  may  be  upheaved  in  the  form  of 
a  ridge  or  cone  without  submarine  eruption.  Since  the  earthquakes 
under  the  sea  are  very  numerous,  there  is  a  great  probability  that 
all  these  movements  of  the  sea  should  be  observed  occasionally. 

Major  Button  adopts  the  view  that  the  sea  bottom  sinks  when 
the  sea  withdraws  from  the  shore,  and  I  also  consider  this  the 
most  probable  cause  in  the  great  majority  of  cases.  It  is  the  more 
logical  to  accept  this  view  since  we  now  see  how  a  sinking  of  the 

1  If  such  an  eruption  occurred  the  surface  of  the  sea  would  be  likely  to 
show  evidence  of  it,  by  ejected  pumice,  ashes,  and  other  volcanic  debris. 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  369 


bottom  can  take  place  by  natural  process.  So  long  as  there  was  no 
means  of  explaining  the  subsidence  of  the  bottom  as  a  part  of  a 
general  process  in  nature,  the  acceptance  of  such  a  violent  hypothesis 
presented  great  difficulty. 

To  make  entirely  clear  how  collapse  of  the  bottom  may  occur 
after  the  expulsion  of  the  steam-saturated  lava  from  under  the  bed 
of  the  Andean  trough,  we  may  observe  that  the  release  of  the  in- 
tense pent-up  pressure  must  tend  to  produce  a  sudden  and  somewhat 
violent  cooling  in  the  stratum  from  which  the  lava  is  expelled.  Its 
support  of  the  overlying  bed  of  the  ocean  trough  is  thus  largely 
withdrawn,  and  sinking  may  easily  follow.  If  this  does  not  happen 
in  every  case  (and  we  have  no  reason  to  think  it  so  frequent  an 
occurrence),  it  would  probably  follow  at  certain  intervals,  when  the 
successive  expulsions  of  material  have  reduced  the  underlying 
stratum  of  lava  to  a  state  of  small  density,  in  which  the  medium  is 
filled  very  largely  with  bubbles  of  steam  and  therefore  rapidly  cooled 
when  the  pressure  is  released  by  an  ejection  of  lava.  This  gives,  I 
think,  a  simple  conception  of  a  self-adjusting  system,  such  as  is  so 
often  found  in  nature,  by  which  the  continuous  process  of  expulsion 
of  lava  may  go  on,  and  the  level  of  the  sea  bottom  be  adjusted  auto- 
matically. But  whether  this  is  the  exact  process  or  some  improve- 
ment may  be  suggested  when  our  knowledge  is  more  extended,  it  is 
clear  that  some  such  automatic  mechanism  is  at  work,  and  that  it  has 
operated  in  similar  troughs  all  over  the  world  throughout  geological 
history. 

As  the  water  did  not  withdraw  and  later  return  as  a  great  wave 
during  the  recent  San  Francisco  and  Valparaiso  earthquakes,  we 
know  that  the  sea  bottom  did  not  sink  in  the  case  of  either  of  these 
great  disturbances.  The  expulsion  of  the  lava,  however,  must  leave 
the  sea  bottom  less  stable  and  increase  the  probability  of  its  sinking 
when  the  next  severe  earthquakes  occur  at  these  places.  As  the 
San  Francisco  earthquake  was  much  less  severe  than  that  at  Val- 
paraiso, the  probability  of  the  sea  bottom  sinking  off  the  Californian 
coast  is  much  less  than  off  the  coast  of  Chili ;  yet  such  a  subsidence 
with  the  accompanying  seismic  sea  wave  is  sure  to  come  sooner  or 
later  in  all  places  subject  to  heavy  earthquakes.  In  1812  the  whole 
of  southern  California  was  severely  shaken  by  earthquakes;  on  De- 


370  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

cember  8,  the  water  withdrew  from  the  shore  at  Santa  Barbara,  and 
after  a  short  interval  returned  as  a  great  wave,  which  overflowed  the 
coast  and  did  much  damage  to  life  and  property.  All  cities  situated 
on  such  coasts  should  be  prepared  for  the  emergency  of  a  seismic  sea 
wave — that  is,  there  should  be  a  place  of  refuge  for  the  people,  and 
houses  thus  exposed  to  the  inundations  of  the  sea  should  not  contain 
treasures  and  historical  articles  which  cannot  be  replaced.  A  mu- 
seum, for  example,  should  never  be  built  in  such  an  exposed 
situation. 

Perhaps  a  few  words  may  be  added  in  regard  to  the  handling 
of  ships,  so  many  of  which  have  been  lost  in  the  past,  owing  to  the 
mystery  surrounding  these  great  waves.  In  South  America  the 
people  have  learned  by  bitter  experience  that  when  an  earthquake 
occurs  the  first  thing  to  do  is  to  watch  the  sea.  If  it  begins  to 
withdraw  from  the  shore  they  at  once  flee  to  high  ground,  for  they 
know  that  the  wave  will  follow.  This  same  principle  is  eminently 
applicable  to  commanders  of  ships  in  the  harbor.  On  the  first  indi- 
cation of  the  retreat  of  the  water  from  the  shore  the  ships  should 
be  headed  with  all  possible  speed  for  the  open  sea.  For  if  the  ships 
remain  in  the  harbor  they  may  soon  be  stranded  and  unable  to  move, 
and  sure  to  be  carried  inland  when  the  wave  returns ;  whereas  if  an 
effort  is  made  to  get  out  to  sea,  the  ships  may  ride  over  the  wave 
without  difficulty  and  suffer  no  damage  whatever.  This  rule  is 
easily  applied  to  all  steam  ships,  whether  belonging  to  the  navy  or 
merchant  marine.  Sailing  vessels,  being  less  under  control  than 
steamships,  might  be  unable  to  escape  in  some  cases;  yet,  if  the 
state  of  the  wind  gave  them  the  requisite  motive  power,  even  they 
might  make  the  open  sea.  A  wave  does  not  come  immediately  after 
an  earthquake,  but  something  like  half  an  hour  or  an  hour  after- 
wards, and  this  usually  gives  time  for  escape.  After  the  sea  bottom 
subsides,  the  water  must  flow  from  the  shore  into  the  depression, 
and  then  when  the  water  piles  up,  it  must  again  flow  back  to  land 
to  produce  the  wave ;  and  if  the  ships  are  properly  handled  in  this 
interval,  most  of  them  will  escape  undamaged. 


I9o6.j  SEE— THE  CAUSE  OF  EARTHQUAKES.  371 

IX.     CONCLUDED  THEORY  OF  VOLCANOES. 

§  42.  Other  theories  of  volcanic  action. 

The  four  fundamental  facts  mentioned  in  §  10  have  been  fully 
considered,  and  we  have  found  that  the  hypothesis  of  the  penetra- 
tion of  sea  water  into  the  crust  of  the  earth  affords  a  natural  and 
satisfactory  explanation  of  all  volcanic  phenomena.  Such  hypotheses 
as  the  following :  ( I )  Lava  flowing  out  of  a  molten  interior,  is 
contradicted  by  the  rise  and  fall  of  the  columns  of  lava  in  volcanoes, 
as  if  forced  up  by  the  elastic  pressure  of  steam,  which  also  escapes 
in  eruptions;  (2)  molten  reservoirs,  contradicted  by  the  same  phe- 
nomena; and  moreover  neither  (i)  nor  (2)  enables  us  to  account 
for  the  observed  distribution  of  volcanoes;  (3)  melting  by  relief  of 
pressure,  and  (4)  melting  by  crushing,  encounter  the  same  diffi- 
culties, and  others  besides.  None  of  these  four  hypotheses  can  be 
seriously  considered. 

There  remains  Major  Button's  recent  suggestion  that  radium 
is  the  exciting  cause.  But  the  researches  of  the  Hon.  R.  J.  Strutt 
have  shown  that  all  the  principal  rocks  of  the  earth's  crust,  especi- 
ally granite,  contain  large  quantities  of  radium,  and  since  these 
rocks  underlie  all  the  continents,  we  should  expect  abundant  active 
volcanoes  everywhere  inland  if  radium  were  the  exciting  cause, 
whereas  in  fact  they  appear  in  the  depths  of  the  sea  or  along  the 
shores  of  the  oceans.  The  cause  of  volcanic  action  is  thus  narrowed 
down  to  the  penetration  of  water  into  the  heated  rocks  of  the  earth's 
crust,  and  all  other  hypotheses  may  be  unhesitatingly  rejected. 

We  shall  now  adduce  some  further  considerations  bearing  on 
the  aqueo-igneous  theory^  with  a  view  of  throwing  additional  light 
upon  particular  phenomena. 

§  43.  Certain  objections  to  the  theory  of  the  penetration  of  sea 
water. 

The  beginning  of  this  theory  may  be  traced  back  to  Lucretius, 
and  perhaps  to  Aristotle,1  and  hence  we  shall  first  answer  two  ob- 
jections which  have  been  urged  against  it. 

First,  it  is  held  that  the  temperatures  of  the  lavas  are  too  high, 
2,000°  to  3,000°,  whereas  one  would  expect  the  temperature  to  be 

1  In  more  recent  times  it  has  been  treated  by  Sir  J.  Prestwich,  in  a  paper 
"  On  the  agency  of  water  in  volcanic  eruptions,"  Proc.  Roy  Soc.,  April  16,  1885. 


372  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

no  higher  than  from  700°  to  1,000°.  A  sufficient  answer  to  this 
objection  is  the  pressure  within  the  earth's  crust,  which  removes  the 
depth  of  fusion  to  a  lower  layer  where  the  temperature  is  higher ; 
and,  moreover,  in  all  eruptions  the  temperature  is  no  doubt  greatly 
raised  by  the  violent  churning  the  lava  receives  before  reaching  the 
orifice  of  the  volcano,  and  by  superheated  steam  escaping  through 
it.  The  lava  would  naturally  flow  from  that  depth  at  which  motion 
under  the  earth's  crust  is  easiest,  and  the  temperature  observed  is 
therefore  about  what  should  be  expected. 

Second,  it  is  held  that  the  fractured  portion  of  the  earth's  crust 
which  would  permit  a  ready  penetration  of  water  is  confined  to  a 
layer  not  more  than  five  or  six  miles  deep,  the  great  pressure  lower 
down  operating  to  close  all  crevices ;  and  it  is  therefore  claimed  that 
water  going  down  fifteen  or  twenty  miles  would  penetrate  the  re- 
maining ten  to  fourteen  miles  of  unbroken  rock  with  great  difficulty. 
In  answer  to  this  objection  it  may  be  said  that  the  depth  to  which 
rocks  are  fractured  is  not  certainly  known ;  but  whatever  it  may  be, 
Daubree's  experiments  show  that  the  force  of  capillarity  may  cause 
the  water  and  steam  to  keep  on  descending  till  the  vapor  reaches  a 
temperature  where  it  is  rapidly  absorbed  and  diffused  among  the 
rock,  just  as  gases  are  in  hot  steel ;  and  when  the  vapor  becomes 
superheated  its  explosive  violence  is  greatly  increased,  and  hence 
this  also  would  tend  to  raise  the  observed  temperature  of  the  lava, 
because  it  is  chiefly  the  hotter  lava,  still  further  heated  in  ejection, 
which  would  be  forced  out  of  volcanoes. 

These  objections,  therefore,  present  no  serious  difficulty  to  the 
theory  that  volcanic  action  depends  on  nothing  but  the  penetration 
of  sea  water. 

It  is  sometimes  said  that  earthquakes  accompanying  volcanic 
eruptions  are  shallow,  and  it  has  therefore  been  inferred  that  the 
lava  comes  from  no  great  depth.  Perhaps  a  more  correct  view 
would  be  to  hold  that  the  throat  of  the  volcano  does  not  be- 
come closed  to  a  great  depth,  by  partial  cooling  of  rock  since  the 
last  eruption,  and  the  shocks  naturally  proceed  from  this  point  of 
resistance  rather  than  from  the  source  of  the  steam  and  lava  rising 
beneath  the  volcano,  which  may  be  much  deeper,  and  yet  give  no 
sensible  indication  of  their  movement  till  the  resistance  becomes  con- 


19o6.j  SEE— THE  CAUSE  OF  EARTHQUAKES.  373 

siderable.  Besides  the  honeycombed  pumice  which  underlies  vol- 
canoes, it  may  be  supposed  that  they  frequently  contain  a  certain 
number  of  passages  out  of  which  the  pumice  has  been  blown,  some 
of  which  may  become  real  caverns  when  the  lava  subsides  after  an 
eruption.  When  a  new  eruption  begins  these  old  passages  might 
offer  little  resistance  till  the  lava  column  came  within  a  short  dis- 
tance of  the  surface,  and  hence  the  shallowness  of  the  shocks  wit- 
nessed in  eruptions.  The  shallowness  of  these  shocks  does  not 
prove  the  superficial  character  of  the  lava  erupted;  on  the  contrary 
the  earthquake  shocks  felt  over  the  whole  region  around  every 
active  volcano  shows  that  the  subterranean  disturbances  arise  in  a 
layer  which  acts  as  fluid  just  beneath  the  crust.  The  forces  de- 
veloping in  this  layer  find  their  relief  in  the  eruption  of  steam  and 
lava  from  the  volcano. 

§  44.  The  origin  of  volcanic  ashes  due  principally  to  the  break- 
ing and  grinding  up  of  pumice. 

In  his  useful  work  on  the  "  Volcanoes  of  North  America,"  the 
late  Professor  Russell,  of  the  University  of  Michigan,  makes  the 
following  explanation  of  the  origin  of  volcanic  ashes  (pp.  75—76)  : 

"  Sheets  of  Volcanic  Sand  and  Dust. — In  the  case  of  volcanic  eruptions 
of  the  explosive  type,  the  steam  occluded  in  the  lava  expands  as  external  pres- 
sure is  relieved ;  this  expansion  is  frequently  so  violent  that  the  rock  is  dis- 
integrated and  the  fragments  projected  high  in  the  air.  Besides  this  primary 
mode  of  reducing  the  lava  to  fragments,  and  much  of  it  to  the  condition  of 
dust,  the  larger  fragments  as  they  are  shot  upwards  with  a  velocity  in  some 
instances  even  greater  than  the  initial  velocity  of  shells  fired  from  modern 
rifle-cannon,  strike  against  one  another  and  against  falling  fragments,  and 
are  shattered,  thus  tending  to  increase  the  quantity  of  fine  dust-like  particles 
produced.  While  much  fine  material  originates  thus,  and  is  carried  away 
by  the  wind,  many  of  the  fragments  that  escape  comminution  fall  into  the 
the  crater  from  which  they  were  thrown  and  are  again  violently  ejected, 
thus  multiplying  the  chances  of  their  being  reduced  to  powder.  An  erup- 
tion of  the  explosive  type  thus  tends  to  form  much  fine  dust,  which  is  car- 
ried high  into  the  air  by  the  upward  rushing  steam  and  falls  most  abundantly 
near  the  place  of  discharge.  Should  a  strong  wind  be  blowing,  the  dust  is 
carried  to  leeward  of  the  volcano,  and  on  reaching  the  earth  forms  a  sheet, 
which,  owing  to  the  winnowing  action  of  the  wind,  is  composed  of  finer  and 
finer  fragments,  the  greater  the  distance  from  the  volcano.". 

Professor  Russell  appreciated  more  fully  than  many  geologists 
the  necessity  of  explaining  the  enormous  clouds  of  dust  which 
arise  from  volcanoes,  but  it  is  difficult  to  escape  the  impression 


374  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October^, 

that  his  explanation  is  somewhat  labored.  It  would  be  more  natural 
to  say  that  a  volcanic  mountain  is  underlaid  and  filled  with  pumice 
and  when  the  explosions  become  violent  some  of  this  porous  ma- 
terial is  ground  up  and  blown  out  as  dust.  Much  of  it  may  already 
be  in  the  form  of  powder  from  former  earthquake  shocks  when  the 
mountain  was  packed  with  pumice,  and  simply  requires  to  be  blown 
out;  and  hence  the  vast  clouds  which  obscure  the  sun  and  darken 
the  earth  for  hundreds  of  miles !  If  the  rock  broken  up  by  the 
explosion  were  solid,  as  supposed  by  Russell,  it  would  be  less  easy 
to  account  for  the  enormous  outpourings  of  ashes,  observed  in 
such  volcanoes  as  Hecla,  yEtna,  Vesuvius  and  Conseguina.  Solid 
rocks  would  produce  lapillse  and  sand  rather  than  fine  ashes,  which 
result  from  the  breaking  up  of  pumice  with  very  thin  bubbles. 

When  lava  is  forced  up  in  the  throat  of  a  volcano  some  of  it 
may  run  out,  relieving  the  pressure  which  raised  it,  and  the  rest 
then  sinks  back  into  some  of  the  passages  which  lead  to  the  throat 
of  the  volcano.  There  may  be,  and  in  general  probably  are,  several 
of  these  passages,  unequally  opened  at  different  times,  and  the  lava 
is  forced  up  from  some  of  them.  After  the  lava  is  poured  out  and 
subsides,  other  passages  formerly  closed  may  be  opened  and  eject 
vast  quantities  of  volcanic  ashes  without  encountering  any  molten 
rock  whatever.  It  would  be  a  great  mistake  to  suppose  that  all 
ashes  which  pour  from  a  volcano  are  forced  through  a  layer  of 
liquid  lava  before  ejection.  If  the  ashes  were  forced  through  a 
layer  of  liquid  they  would  be  red  hot  when  cast  out,  and  such  heat 
would  give  the  particles  a  ruddy  glow.  As  a  general  rule,  such  a 
glow  is  not  observed,  and  hence  the  theory  that  the  ashes  are  ejected 
through  a  layer  of  liquid  is  untenable.  The  outpouring  of  lava  is 
only  a  part  of  the  operations  of  a  volcano;  the  ejection  of  vapor, 
ashes  and  pumice  being,  perhaps,  even  more  important.  Steam  is 
the  one  force  which  has  to  be  relieved,  and  the  other  substances 
ejected  are  incidental  thereto. 

In  his  well-known  on  "Geology"  (fourth  edition,  1903),  p. 
173,  Sir  Archibald  Geikie  says: 

"...  The  finest  dust  is  in  a  state  of  extremely  minute  subdivision. 
When  examined  under  the  microscope,  it  is  sometimes  found  to  consist  not 
only  of  minute  crystals  and  microlites,  but  of  volcanic  glass,  which  may  be 
observed  adhering  to  the  microlites  or  crystals  round  which  it  flowed  when 


I9o6<]  SEE— THE  CAUSE  OF  EARTHQUAKES.  375 

still  part  of  the  fluid  lava.  The  presence  of  minutely  cellular  fragments  is 
characteristic  of  most  volcanic  fragmental  rocks,  and  this  structure  may 
commonly  be  observed  in  the  microscopic  fragments  and  filaments  of  ghss. 
A  characteristic  feature  of  these  minute  fragments  is  the  frequent  occur- 
rence among  them  of  semi-circular  or  elliptical  ('hour-glass')  shapes,  which 
evidently  represent  the  sides  of  vesicles  or  pores  that  enclosed  vapour  or 
gas  in  the  molten  rock,  and  were  disrupted  and  blown  out  during  volcanic 
explosions." 

§  45.  On  the  supposed  absence  of  volcanoes  in  the  Alps  and 
Himalayas,  and  on  the  former  existence  of  these  vents  in  the  interior 
of  continents. 

It  is  frequently  remarked  that  volcanoes  do  not  appear  in  the 
Alps  and  Himalayas,  and  the  inference  has  been  drawn  that  no 
volcanoes  originated  in  the  formation  of  these  great  mountain 
ranges.  But  it  is  well  known  that  at  some  time  in  the  past  geological 
ages  volcanoes  existed  in  almost  every  part  of  every  country,  and 
mountain  chains  like  the  Alps  and  Himalayas  are  no  exceptions  to 
the  general  rule.  Professor  Suess  ("  Face  of  the  Earth,"  Vol.  I, 
pp.  201-274)  mentions  some  volcanoes  formerly  active  in  the  Alps, 
and  undoubtedly  similar  vents  once  existed  in  the  Himalayas.  In 
the  course  of  time  nearly  all  surface  trace  of  eruptions  is  lost 
where  the  glaciation,  denudation  and  sedimentation  are  active,  as  in 
the  Himalayas.  When  we  consider  how  imperfect  our  knowledge 
of  those  mountains  is,  not  only  because  they  are  high,  but  also 
inaccessible  to  exploration,  the  failure  up  to  this  time  to  find  extinct 
volcanoes  or  their  products  is  not  remarkable.  Craters  are  soon 
covered  by  ice  and  worn  down  by  the  grinding  action  of  glaciers, 
while  their  ashes  and  lavas  are  equally  covered  and  lost  from  view. 

Major  Dutton  justly  remarks  that  the  regions  which  have  been 
exempt  from  volcanoes  are  small  in  comparison  with  those  which 
have  had  them;  and  he  observes  that  going  back  to  early  Tertiary 
times  we  find  them  occurring  where  they  have  long  been  extinct. 

"  The  grandest  volcanic  field  in  the  world  was  central  and  southern  India 
in  Cretaceous  times,  when  there  was  not  a  volcano  in  all  Europe,  and  ex- 
tremely few  in  North  and  South  America.  In  the  Jura-Trias,  the  Appa- 
lachian region,  from  Labrador  to  the  Gulf  of  Mexico,  bristled  with  them, 
and  vast  plateaux  of  lava  were  outpoured.  In  Paleozoic,  they  abounded  in 
the  region  of  the  Great  Lakes,  in  Missouri,  in  Arkansas,  and  in  eastern  Texas. 
There  is  hardly  a  county  or  bailiwick  on  the  whole  mundane  sphere  which 
has  not  had  its  volcanic  cycle  at  some  time  or  other,  and  there  are  many 

PROC.  AMER.  PHIL.  SOC.,  XLV.    184  X,  PRINTED  FEBRUARY  25,   1907 . 


376  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19 

which  have  had  two,  three,  four  or  five  cycles.  Volcanoes  are  not  local 
phenomena,  nor  yet  are  they  strictly  universal.  But  they  come  very  near 
being  universal.  I  think  that  Charles  Darwin's  observation  that  they  are 
associated  with  regions  of  elevation  is  very  generally  sustained,  even  in  the 
depths  of  the  ocean." 

These  remarks  of  Major  Button,  communicated  to  the  writer  in 
a  private  letter,  are  of  unusual  interest.  At  the  present  time  we 
have  no  active  volcano  in  the  world  more  than  100  miles  from  the 
sea  or  equivalent  large  body  of  water.  It  has  been  remarked  that 
Mt.  Demavend  is  about  320  miles  from  the  Mediterranean,  but  only 
about  50  miles  from  the  Caspian  Sea,  which  is  a  deep  body  of  salt 
water.  In  the  same  way  Jorullo  in  Mexico  is  about  80  miles  from 
the  Pacific  coast,  but  it  has  never  been  active  since  the  first  out- 
break in  1759.  Some  of  the  volcanoes  in  the  eastern  range  of  the 
Andes  of  Bolivia  may  be  over  100  miles  from  the  sea,  but  they  are 
much  nearer  Lake  Titicaca  and  the  terrible  tropical  rains  which 
constantly  drench  the  eastern  slopes  of  the  Andes. 

Thus  all  active  volcanoes,  to  the  number  of  about  400,  are  very 
near  the  sea  or  equivalent  large  lakes.  In  the  interior  of  continents 
they  die  out  for  lack  of  adequate  water  supply.  Unfortunately, 
we  do  not  know  the  contours  of  the  sea  in  past  geological  ages  very 
accurately,  but  from  Major  Button's  remarks,  quoted  above,  it  seems 
probable  that  volcanoes  have  always  developed  in  the  neighborhood 
of  the  sea  and  died  out  when  the  water  receded  to  a  considerable 
distance  from  them.  This  is  well  illustrated  by  the  extinct  volcanoes 
now  found  in  the  western  part  of  the  United  States.  Thus  volcanoes 
of  former  ages  seem  to  follow  the  same  law  as  those  now  active. 

The  present  distribution  of  volcanoes  proves  conclusively  that 
they  depend  upon  the  sea.  The  erupting  force  is  shown  to  be  steam 
by  the  great  preponderance  (999  parts  in  1,000)  which  that  vapor 
has  over  all  others. 

The  progressive  extinction  of  volcanoes  in  the  interior  of 
continents  is,  therefore,  clearly  intelligible.  Not  only  do  the  vol- 
canoes die  out  for  lack  of  motive  power  to  keep  open  the  orifices, 
but  the  earthquakes  also  famish  in  the  same  way,  though  to  a  lesser 
degree,  because  their  explosive  force  is  distributed  over  a  wider 
area  and  does  not  require  to  be  so  concentrated.  Unless  a  volcano 
keeps  moderately  active  it  becomes  permanently  closed  by  lava 


I9o6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES.  377 


hardening  in  its  throat ;  yet  earthquakes  which  have  no  surface  out- 
let may  successfully  maintain  a  languid  existence  on  a  small  supply 
of  water,  and  hence  they  may  continue  to  be  felt  in  a  region  long 
after  all  volcanoes  have  been  extinguished. 

§  46.  Explanation  of  immense  outflows  of  lava  such  as  are  seen 
in  the  plateau  of  Deccan  and  in  Oregon  and  Utah. 

For  a  number  of  years  it  has  been  a  subject  of  remark  among 
geologists  that  the  largest  lava  flows  are  not  the  output  of  volcanoes, 
but  of  immense  fissures  which  opened  in  the  earth's  crust  and  per- 
mitted the  welling  forth  of  vast  quantities  of  molten  rock.  Sir 
Archibald  Geikie  (cf.  Suess,  Vol.  I,  p.  145)  emphasized  this  view 
as  long  ago  as  1880.  In  recent  years  this  theory  of  the  origin  of  the 
immense  deposits  of  sheet  lava  seen  in  the  region  of  the  Columbia 
River  in  Oregon  and  in  Utah,  as  well  as  in  the  great  tableland  of 
Deccan  in  India,  has  been  very  generally  adopted.  In  all  such  cases 
fissures  no  doubt  opened  and  poured  forth  the  molten  rock  through- 
out their  length.  The  subsidence  of  considerable  areas  of  the  earth's 
crust  may  have  contributed  to  this  outflow,  and  different  degrees 
of  liquidity  are  invoked  to  explain  the  observed  phenomena.  Reyer 
suggests  (cf.  Geikie's  "Geology,"  Vol.  I,  p.  301)  that  the  degree 
of  saturation  with  gases  and  vapors  may  have  influenced  the  form 
of  eruption,  volcanic  discharges  resulting  when  the  impregnation 
was  strong  enough  to  cause  eruption,  and  tranquil  outpourings  whea 
the  rock  is  but  feebly  saturated  with  explosive  gases. 

Major  Dutton  thinks  differences  of  temperature  as  well  as 
chemical  differences  may  have  been  more  important  in  giving  the 
great  lava  flows  their  peculiar  aspects.  In  regard  to  these  outflows 
in  general,  I  believe  that  the  crust  cracked  open  on  account  of 'the 
relative  movement  of  neighboring  portions.  There  are  many  ways 
in  which  this  could  occur.  If  there  were  any  appreciable  tangential 
pressure  between  two  portions  of  the  crust,  the  outpouring  of  lava 
would  be  less  easy ;  but  since  we  abandon  the  contraction  theory  and 
deny  that  the  mountains  are  due  to  the  shrinkage  of  the  crust,  there 
is  on  this  hypothesis  no  pressure  between  the  two  portions  of  the 
crust  except  that  due  to  their  weight  when  resting  side  by  side.  If, 
therefore,  the  subterranean  movements  under  two  neighboring  parts 
should  be  such  as  to  force  a  fault  apart,  there  would  be  nothing  to 
prevent  the  lava  from  rising  and  pouring  forth. 


378  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

In  the  valley  of  the  Ganges  the  earthquake  thrusts  were  towards 
the  Himalayas,  and  at  some  period  in  the  upheaval  of  these  moun- 
tains the  crust  may  have  been  cracked  and  also  so  pulled  apart  as 
to  allow  the  great  lava  flows  observed  in  the  plateau  of  Deccan. 
Much  of  this  may  have  occurred  when  the  peninsula  of  India  was 
still  under  the  sea.  No  doubt  the  great  lava  flows  of  Oregon  and 
Utah  were  similar  in  character,  but  the  details  of  the  process  must 
be  left  to  future  investigation. 

§  47.  On  the  vapors  exhaled  by  volcanoes. 

We  have  seen  that,  according  to  Geikie,  999  parts  in  1,000  of  the 
vapors  emitted  by  volcanoes  is  composed  of  steam,  and  have  con- 
cluded that  this  is  the  only  original  vapor  operating  under  the  earth's 
crust.  For  the  one-thousandth  part  of  other  gases  such  as  sulphur- 
ous oxide,  carbon  dioxide,  hydrochloric  acid,  et  cetera,  may  well 
be  derived  from  the  heated  rocks  when  saturated  with  steam,  with- 
out any  other  original  gas  existing  in  the  earth.  If  any  other  gas 
except  steam  were  really  active  in  the  earth,  either  under  the  vol- 
yanoes  or  in  remote  regions  which  are  disturbed  by  earthquakes,  we 
may  be  very  sure  that  at  some  of  the  volcanoes  some  of  this  gas 
would  escape  and  we  should  be  able  to  recognize  it.  As  such  escape 
does  not  occur  we  may  be  quite  sure  that  steam  is  the  only  original 
vapor  operating  within  the  earth. 

The  question  of  the  dissociation  of  water  vapor  by  the  intense 
heat  of  subterranean  lava  is  also  worthy  of  remark.  It  has  been 
found  by  analyses  of  the  vapors  escaping  from  Thera,  where  the 
outlets  are  generally  submarine,  that  the  water  gases  are  dissociated. 
Immediately  over  the  focus  of  eruption  free  hydrogen  formed  30 
per  cent,  of  the  gases  emitted.  In  general  the  free  hydrogen  is  fully 
twice  as  abundant  as  the  free  oxygen,  so  that  the  mixture  on  coming 
in  contact  with  a  burning  body  at  once  ignites  with  a  sharp  ex- 
plosion. A  considerable  quantity  of  free  nitrogen  is  also  present, 
and  traces  of  other  gases.  Fouque,  who  has  given  most  attention 
to  this  subject,  infers  that  the  water- vapor  of  volcanic  vents  may 
exist  in  a  state  of  dissociation  in  the  magma  just  beneath  the  earth's 
crust.  The  free  nitrogen  is  supposed  to  be  derived  from  the  air 
absorbed  in  the  water  which  percolates  downward. 

The  question  of  the  existence  of  true  volcanic  flames  was  first 


X9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  379 

settled  by  the  observations  of  Fouque,  who  showed  that  true  flames 
may  arise  when  the  free  gaseous  mixtures  are  ignited  by  red  hot 
stones  from  the  volcano  or  by  the  strokes  of  lightning  which  play 
so  actively  about  the  orifice  of  a  volcano  in  eruption.  No  doubt  the 
dreadful  tongues  of  fire  so  often  seen  to  radiate  from  erupting  vol- 
canoes are  to  be  explained  very  largely  by  the  ignition  of  free  gases 
by  thunderbolts  produced  by  the  condensation  of  clouds  of  aqueous 
vapor. 

§  48.  Strabo  speaks  of  the  volcanoes  as  safety  valves. 

In  his  "  Principles  of  Geology,"  12  edition,  Vol.  I,  p.  25,  Lyell 
remarks  that  the  gifted  Amasean  geographer,  Strabo,  alluding  to  the 
•tradition  that  Sicily  had  been  separated  by  a  convulsion  from  Italy, 
adds  (Lib.  vl,  p.  396,  edit.  Almelov.  Amst.  1707)  that  in  his  time 
the  land  near  the  sea  in  those  parts  was  rarely  shaken  by  earth- 
quakes, since  open  orifices  exist  whereby  fire  and  burning  matter 
and  water  escape ;  but  formerly,  when  the  volcanoes  of  ^Etna,  the 
Lapari  Islands,  Ischia  and  others  were  closed  up,  the  imprisoned 
fire  and  wind  might  have  produced  far  more  vehement  movements. 
"  The  doctrine,  therefore,"  continues  Lyell,  "  that  volcanoes  are 
safety  valves,  and  that  the  subterranean  convulsions  are  probably 
most  violent  when  first  the  volcanic  energy  shifts  itself  to  a  new 
quarter,  is  not  modern." 

X.     CONCLUDED  THEORY  OF  EARTHQUAKES. 

§  49.  All  important  earthquakes  due  to  the  action  of  explosive 
forces  within  or  just  under  the  earth's  crust. 

Major  Dutton  seems  to  have  had  an  inkling  of  the  process  here 
involved  when  he  wrote  the  following  ("  Earthquakes,"  p.  49-5°)  : 

Fit  remains  now  to  refer  to  the  possibility  that  many  quakes  whose 
origin  is  unknown,  or  extremely  doubtful,  may,  after  all,  be  volcanic.  This 
must  be  fully  admitted,  and  indeed,  it  is  in  many  cases  highly  probable. 
Evidences  that  volcanic  action  has  taken  place  in  the  depths  of  the  earth  with- 
out visible,  permanent  results  on  the  surface  abound  in  ancient  rock  ex- 
posures. Formations  of  great  geological  age,  once  deeply  buried  and 
brought  to  daylight  by  secular  denudation,  show  that  lavas  have  penetrated 
surrounding  rock-masses  in  many  astonishing  ways.  Sometimes  they  have 
intruded  between  strata,  lifting  or  floating  up  the  overlying  beds  without  any 
indication  of  escaping  to  the  surface.  Sometinies  the  lava  breaks  across  a 
series  of  strata  and  finds  its  way  into  the  partings  between  higher  beds.  Or 


380  SEE  -THE  CAUSE  OF  EARTHQUAKES. 


[October  19, 


it  forces  its  way  into  a  fissure  to  form  a  dyke  which  may  never  reach  the 
surface.  In  one  place  a  long  arm  or  sheet  of  lava  has  in  a  most  surprising 
and  inexplicable  manner  thrust  itself  into  the  enveloping  rock-mass,  and  in 
the  older  of  metamorphic  rocks  these  offshoots  or  apophyses  cross  each  other 
in  great  numbers  and  form  a  tangled  network  of  intrusive  dykes.  In  other 
places  the  intruded  lava  formed  immense  lenticular  masses  (laccolites),  which 
have  domed  up  the  overlying  strata  into  mountain  masses.  These  intrusions, 
almost  infinitely  varied  in  form  and  condition,  are  often,  in  fact  usually,  in- 
explicable as  mechanical  problems,  but  their  reality  is  vouched  for  by  the 
evidence  of  our  senses.  What  concerns  us  here  is  the  great  energy  which 
they  suggest  and  their  adequacy  to  generate  in  the  rocks  those  sudden,  elastic 
displacements  which  are  the  real  initiatory  impulses  of  an  earthquake.  They 
assure  us  that  a  great  deal  of  volcanic  action  has  transpired  in  past  ages  far 
underground,  wrhich  makes  no  either  sign  at  the  surface  than  those  vibrations 
which  we  call  an  earthquake."  <$>  ^  ^^ 

The  blowing  out  of  a  huge  obelisk  of  granite  some  300  meters 
long  and  120  meters  in  diameter  but  too  large  to  get  through 
the  orifice  of  Mount  Pelee,  and  which  therefore  hung  in  the  mouth  of 
that  volcano,  while  the  cone  itself  was  split  on  all  sides  by  the  fearful 
force  of  the  explosion  which  had  ejected  the  plug  of  granite  from 
the  roots  of  the  volcano,  affords  an  excellent  and  familiar  example 
of  what  may  be  done  by  volcanic  forces.  This  obelisk  is  illustrated 
in  the  National  Geographic  Magazine  for  August,  .1906,  by  photo- 
graphs made  by  Professor  A.  Heilprin,  who  gives  an  excellent  ac- 
count of  the  history  of  the  obelisk  and  its  gradual  disintegration. 
If  these  forces  are  suddenly  arrested,  as  they  are  in  all  earthquakes 
which  do  not  produce  immediate  eruptions,  the  shock  is  taken  up  by 
the  surrounding  earth  and  we  have  a  violent  earthquake  which  may 
be  felt  all  over  the  world. 

If  the  explosions  are  no  larger  than  those  involved  in  the  erup- 
tions of  geysers  the  results  are  mere  microseisms  or  earth  tremors, 
interesting  enough  to  be  sure,  but  of  an  unimportant  character.  A 
really  serious  earthquake,  to  be  felt  all  over  the  world,  implies  the 
exertion  of  the  most  tremendous  forces,  and  the  way  in  which  these 
forces  set  the  earth  particles  vibrating  shows  that  they  must  depend 
primarily  upon  the  explosive  power  of  steam-saturated  lava  at  great 
temperature.  The  result  is  a  violent  shaking  of  the  whole  overlying 
layers  of  rock  and  the  occasional  upheaval  of  volcanoes  where  the 
strata  are  fractured  and  weak.  The  very  way  in  which  the  earth 
twists,  heaves,  labors  and  vibrates  shows  the  awfulness  of  the  pent-up 


igo6.] 


SEE— THE  CAUSE  OF  EARTHQUAKES. 
FIG.  15. 


381 


The  shattered  obelisk  of  Mt.  Pelee,  photograph  taken  by  Professor 
Angelo  Heilprin. 

forces;  and  it  is  no  wonder  that  such  shaking  should  throw  down 
buildings,  settle  soft  "  made  "  ground,  leaving  fissures  where  it  is 
shaken  down,  and  even  cause  faults  in  the  overlying  mountains  to 
slip  or  open. 

§  50.  But  the  movements  of  faults  are  the  effects  of  the  earth- 
quake, not  the  cause. 

Such  small  slips  as  are  usually  observed  would  not  account  for 
the  enormous  forces  shown  in  the  accompanying  earthquakes.  Be- 
sides the  horizontal  form  of  the  vibrations,  so  frequently  shown,  as 
more  fully  pointed  out  in  §  51,  could  not  be  explained  by  simple 


382 


SEE— THE  CAUSE  OF  EARTHQUAKES. 


[October  19, 


subsidence.  Yet  it  is  evident  that  these  faults  may  easily  result  from 
the  mighty  steam  pressure  which  has  shaken  the  earth  sufficiently  to 
break  the  layers  of  rock,  and  give  relief  to  the  pent-up  forces.  In 
so-called  tectonic  earthquakes  the  forces  usually  are  greater  than 
those  involved  in  volcanic  action,  because  the  whole  body  of  the 
overlying  strata  must  be  shaken  to  afford  the  smallest  relief,  but  are 
seldom  so  concentrated  as  would  be  required  for  the  upheaval  of  a  new 
volcano  through  the  entire  depth  of  the  unbroken  crust.  If  the  crust 
is  already  badly  fractured  or  breaks  more  easily  than  it  gives  relief 

FIG.  1 6. 


when  shaken,  sometimes  new  volcanoes  actually  break  forth,  especi- 
ally under  the  sea,  where  the  explosive  forces  are  greatest. 

When  we  consider  the  terrific  shock  required  to  break  all  the 
horizontal  strata  in  a  situation  where  the  imprisoned  forces  are 
deep-seated  we  can  readily  imagine  that  yielding  will  often  occur 
through  condensation  of  soft  rocks,  through  tightening  up  of  crev- 
ices, joints  and  faults,  and  sometimes  by  uplifts  of  all  the  strata, 
affording  room  for  the  injection  of  a  layer  of  lava  of  large  extent, 
or  its  diffusion  by  spreading  into  surrounding  areas.  The  move- 
ment of  the  fluid  is  shown  by  the  arrows  in  the  figure.  In  that  case 


i9o6  1  SEE— THE  CAUSE  OF  EARTHQUAKES.  383 

the  eruptions  may  be  either  subterranean  or  submarine,  as  in  the 
elevation  of  the  Chilean  coast  noticed  by  Darwin  and  Fitzroy  in  1835. 

On  the  theory  of  faults,  as  now  held,  it  is  difficult  if  not  im- 
possible to  account  for  the  observed  elevations.  It  is  perhaps  true 
that  elevations  apparently  are  rarer  than  subsidences,  yet  they 
are  much  more  significant  and  furnish  a  better  criterion  of  the  forces 
at  work,  since  many  subsidences  on  land  are  due  to  settling  of  soft 
ground  which  has  never  been  consolidated  under  pressure.  But 
we  must  remember  that  only  very  few  absolute  levels  are  accurately 
known  and  still  fewer  remeasured  after  an  earthquake ;  and  therefore 
while  subsidences  appear  to  be  the  more  general  phenomena,  espe- 
cially in  regions  of  soft  earth,  one  may  well  be  very  doubtful  whether, 
in  the  case  of  hard  ground,  elevations,  though  mostly  unnoticed 
because  there  is  no  easy  means  of  measurement,  do  not  really  pre- 
dominate. Reasons  connected  with  the  mode  of  formation  of  moun- 
tains and  the  elevation  of  coast  lines,  given  heretofore,  point  strongly 
to  elevation  as  the  more  general  movement  in  nature.  For  it  is  this 
movement  which  has  uplifted  both  mountains  and  continents,  and  we 
cannot  suppose  that  it  has  ceased  to  be  the  dominant  influence, 
though  it  generally  escapes  notice,  because  we  have  no  means  of 
detecting  it,  while  local  subsidences  frequently  are  easily  recognized, 
and  we  naturally  look  for  it  because  of  the  frequent  shaking  down  of 
"  made  "  ground. 

In  most  earthquakes  the  heaving  force  is  distributed  over  a 
considerable  area,  and  when  the  stress  becomes  great  enough  a 
movement  takes  place  along  the  nearest  fault  line — the  path  of  least 
resistance — and  the  observer  who  sees  the  slip  says  the  movement 
of  the  fault  caused  the  earthquake. 

The  fact  that  most  earthquakes  are  found  to  originate  at  a  depth 
of  from  ten  to  twenty  miles  shows  that  the  epicentrum  is  below  the 
depth  at  which  the  strata  have  any  opportunity  of  moving;  and  the 
proof  that  the  shock  usually  comes  from  an  area  and  not  from  a 
point  or  from  a  line,  shows  that  the  shock  depends  on  an  explosive 
stress  spread  over  a  considerable  region,  and  in  no  way  depends  on 
dislocational  or  fault  movements,  which  are  always  quite  superficial. 

§51.  Explanation  of  the  rotatory  motion  observed  during  an 
earthquake. 


384  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  i9f 

If  we  consider  with  attention  how  simple  the  motion  of  sub- 
sidence or  elevation,  in  a  supposed  fault,  really  is,  we  shall  per- 
ceive that  such  displacement  cannot  give  the  earth  particle  an  ap- 
preciable rotatory  motion.  For  the  two  sides  of  a  fault  are  con- 
ceived as  continuous  and  unbroken  parts  of  the  earth's  crust,  and 
thus  securely  fixed  at  their  backs,  and  moving  only  at  their  faces, 
where  the  fracture  exists.  The  motion  is  essentially  like  that  of 
a  double  cellar  door  opening  or  closing  very  slightly  in  the  middle, 
with  rigid  hinges  at  their  backs.  They  can  only  go  up  or  down 
together,  or  one  up  and  one  down,  with  little  or  no  horizontal 
motion;  and  thus  cannot  produce  a  revolving  tremor  when  opened 
or  shut. 

It  is  exactly  so  with  the  slipping  of  a  supposed  fault  in  the 
earth's  crust.  It  is  mechanically  inconceivable  how  the  vertical  sub- 
sidence of  a  fault  could  give  the  earth  particle  a  revolving  motion  in 
the  plane  of  the  horizon.  At  most,  such  a  slip  could  produce  an 
up-and-down  oscillation,  with  the  path  of  the  ellipse  described  by 
the  particle  very  nearly  in  the  vertical  plane. 

Now  the  earthquake  which  destroyed  San  Francisco  gave  the 
earth  particle  a  large  and  conspicuous  rotation  almost  parallel  to 
the  horizon ;  it  was  "  a  twister,"  and  this  rotatory  character  was 
so  marked  as  to  attract  instant  attention.  The  conspicuous  rota- 
tion and  the  difficulty  of  explaining  such  a  motion  by  the  theory  of 
faults,  as  ordinarily  stated,  led  the  writer  to  question  the  validity 
of  that  theory.  As  most  of  the  violent  earthquakes  have  both  rota- 
tion and  vertical  movement,  it  is  evident  that  the  difficulty  felt  in 
explaining  the  San  Francisco  earthquake  is  very  generally  encoun- 
tered in  earthquake  phenomena. 

It  seems  to  have  escaped  the  attention  of  seismologists  that 
rotatory  earthquakes  require  explanation,  and  the  theory  of  subsi- 
dences of  rocks  and  faults  is  incapable  of  furnishing  it.  How  then 
can  motion  of  rotation  be  accounted  for? 

To  answer  this  question  in  the  simplest  way  we  may  recall  that 
there  are  many  impulses  which  can  give  a  motion  of  rotation,  either 
by  direct  impact  or  by  the  "  kick  back,"  or  recoil  of  reaction.  If, 
for  example,  we  suppose  an  orifice  to  be  forced  through  an  under- 
lying or  overlying  layer  of  rock  so  that  lava  escapes  under  great 


I9o6.] 


SEE-THE  CAUSE  OF  EARTHQUAKES. 


385 


pressure,  but  the  resistance  is  unequal  in  the  different  directions, 
it  is  evident  that  as  the  imprisoned  matter  expands  or  explodes,  the 
reactions  in  the  different  directions  will  be  inversely  as  the  corre- 
sponding resistances  to  the  escaping  fluid.  In  general  the  explosion 
will  give  a  rotation  to  the  surrounding  particles,  since  the  moment 

FIG.  17. 


Seismographic  record  of  the  San  Francisco  Earthquake,  April  18,  1906, 
taken  at  the  Chabot  Observatory,  Oakland,  California,  Professor  Charles 
Burkhalter,  Director. 

of  the  resistances  will  not  pass  exactly  through  the  center  of  the 
exploding  mass,  and  the  rotation  is  as  likely  or  more  likely  to  be 
in  the  horizontal  plane  than  in  any  other.  If  the  explosion  or  rapid 
diffusion  of  steam  pressure  takes  place  in  stratified  rock,  the  strata 
are  fairly  sure  to  be  approximately  horizontal ;  but  no  doubt  most  all 


386  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19 

violent  earthquakes  occur  at  greater  depths,  and  no  one  can  predict 
the  inequalities  of  the  encountered  resistance.  It  would  all  depend 
on  the  shape  and  relative  situation  of  the  expanding  matter  in  rela- 
tion to  the  surrounding  rock,  which  would  also  be  at  high  tem- 
perature. 

As  the  reservoir  of  steam-saturated  lava  would  rarely  be  spherical 
and  would  usually  be  a  layer,  as  we  have  seen  in  part  IV,  and  several 
separate  and  distinct  reservoirs  might  develop  near  one  another, 
a  streaming  of  the  released  matter,  when  the  walls  yielded  and  the 
strain  is  released  and  the  fluid  quickly  adjusted  itself  to  the  new 
surroundings,  would  almost  always  produce  some  kind  of  rotatory 
motion,  and  it  would  always  lie  in  a  plane  between  the  horizon  and 
the  zenith.  If  the  layers  were  complex  or  of  irregular  figure  this 
movement  might  be  made  up  of  several  parts  and  the  adjustment 
occupy  several  seconds,  and  possibly  minutes,  of  time,  even  when 
the  forces  are  enormous  and  the  motion  correspondingly  rapid. 

The  successive  powerful  impulses  or  blows  imparted  to  the  sur- 
rounding earth  might  be  of  unequal  intensity  and  not  all  in  the  same 
plane,  and  moreover  the  vibration  would  continue  for  a  short  time 
after  the  internal  movement  had  ceased,  on  account  of  the  elasticity 
of  the  rocks  of  the  earth's  crust.  Lava  saturated  with  superheated 
steam  would  behave  essentially  like  steam  in  an  exploding  boiler, 
because  it  would  give  body  and  momentum  to  the  spreading  steam 
and  be  capable  of  transmitting  shocks  of  appalling  violence. 

This  gives  us  a  conception  not  only  of  the  process  involved  in  an 
earthquake,  but  also  of  how  the  irregularities  noted  by  seismographs 
might  be  accounted  for;  and  when  we  recall  that  the  subterranean 
boiler  might  surpass  the  largest  mountain  in  size,  or  be  flattened 
into  an  immense  disc1  of  slight  thickness,  with  vent  chiefly  or 
wholly  at  the  sides,  we  can  easily  understand  the  terrific  forces 
which  shake  the  whole  earth  when  once  the  surrounding  walls  give 
way  or  a  fault  moves,  so  that  an  explosion  and  diffusion  of  the  lava 
is  effected. 

It  must  be  assumed,  for  reasons  already  fully  developed,  that 
sensible  readjustment  and  motion  of  large  masses  of  steam-saturated 

1  It  is  found  by  investigation  that  many  of  the  tectonic  earthquakes  origi- 
nate in  an  area  of  considerable  extent. 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  387 

lava  or  molten  rock  take  place  in  every  important  earthquake ; 
confining  walls  and  caverns  of  unequal  pressure  are  reduced  to  one 
common  strain,  and  the  resulting  motion  involves  rapidly  acting 
and  enormously  powerful  forces,  which  may  shake  the  whole  earth 
and  sometimes  crack  or  derange  the  overlying  strata  of  rocks  many 
kilometers  deep. 

§  52.  Explanation  of  the  New  Madrid  earthquake  and  some 
other  earthquakes  often  classed  as  tectonic. 

In  his  excellent  work  on  "  Earthquakes  "  Major  Button  remarks 
that  the  New  Madrid  earthquake  could  not  be  said  to  have  any  real 
depth,  although  he  says  it  was  strongly  felt  as  far  east  as  Boston, 
and  in  fact  nearly  all  over  the  United  States.  His  reasoning  is 
based  upon  the  supposition  that  it  was  due  to  the  sinking  of  some 
bottom  land,  which  seems  to  be  quite  unjustifiable.  The  subsidences 
happened,  indeed,  but  we  shall  find  the  best  reasons  for  holding 
that  they  were  produced  by  explosions  within  the  earth,  which 
must  therefore  have  been  at  least  ten  miles  deep.  Unless  it  had 
been  of  about  this  depth  this  earthquake  could  not  have  been  so 
strongly  felt  throughout  so  wide  an  area  of  country. 

It  seems  probable  that  the  water  seeped  down  from  the  Mis- 
sissippi River,  which  always  overflowed  badly  here,  and  worse  in 
prehistoric  times  than  now,  because  the  country  was  then  much 
more  heavily  timbered;  or  the  seepage  was  a  survival  effect  of  the 
fractures  of  the  Ozark  Mountains,  from  the  time  when  the  Gulf  of 
Mexico  extended  far  up  the  river,  and  thus  was  beginning  to  form 
a  sea  valley  about  parallel  to  the  general  trend  of  the  Ozark 
Mountains  which  were  left  unfinished. 

Thus  the  cause  producing  this  earthquake  is  apparently  not  dif- 
ferent from  those  at  Charleston,  San  Francisco  and  many  other 
places  which  have  experienced  so-called  tectonic  earthquakes. 

The  most  trustworthy  accounts  of  the  New  Madrid  earthquake 
show  that  it  was  the  most  violent  and  destructive  earthquake  ever 
felt  in  the  United  States.  Lyell  has  given  an  excellent  account  of 
this  earthquake,  based  upon  observations  gathered  during  a  per- 
sonal visit  in  1846,  but  the  records  here  followed  are  of  still  earlier 
date. 

Over  a  region  of  300  miles  in  length,  but  especially  from  the 


388  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

mouth  of  the  Ohio  to  that  of  the  St.  Francis  River,  the  ground  rose 
and  sank  in  great  undulations ;  trees  had  to  be  felled  across  the 
fissures  for  the  preservation  of  the  inhabitants,  and  lakes  were 
formed  and  drained  again,  and  many  large  streams  changed  their 
channels  and  even  their  courses.  Physical  evidences  of  this  terrible 
convulsion  are  still  seen  near  New  Madrid,  where  the  loose  land 
had  settled  so  much  as  to  form  swamps,  leaving  great  cypress  and 
other  trees  so  deep  in  the  water  that  they  died  (some  were  entirely 
submerged),  and  in  many  places  still  remain  to  show  where  the 
water  rose  in  1811.  Little  Prairie,  now  called  Caruthersville,  20 
miles  below  New  Madrid,  was  considered  the  center  of  greatest 
violence.  The  first  severe  earthquake  occurred  on  the  night  of  De- 
cember 1 6,  2:15  a.  m.,  -and  shook  severely  the  whole  region  of  the 
Ohio,  Mississippi  and  Missouri  rivers,  as  far  north  as  the  Lakes,  as 
far  east  as  the  Alleghanies,  south  to  the  gulf,  and  west  to  the 
Rocky  Mountains. 

One  of  the  best  accounts  of  this  great  earthquake,  drawn  from 
contemporary  sources  of  information,  is  that  given  by  Professor  G. 
C.  Broadhead,  of  the  University  of  Missouri,  in  the  American  Geolo- 
gist for  August,  1902.  The  leading  points  may  be  summarized  thus  : 

1.  After  the  first  severe   shock  at  2:15   in  the  night,   smaller 
shocks  followed,  and  at  7  a.  m.,  December  16,  1811,  came  a  much 
more  severe  shock ;  then  came  lighter  shocks  daily  or  oftener,  until 
January  23,  1812,  when  an  extremely  severe  shock  was  felt;  con- 
tinual agitations  were  felt  till  February  4,  which  brought  another 
severe  shock,  and  four  more  followed  next  day ;  and  on  February 
7,  at  4  p.  m.,  came  one  so  much  more  violent  than  the  preceding  that 
it  was  called  "  the  hard  shock."     Hundreds  and  even  thousands  of 
smaller  after-shocks  have   continued  at  irregular  intervals  to  the 
present  time.    "  Two  series  of  the  (original)  concussions  were  par- 
ticularly terrible." 

2.  Thus  there  were  at  least  eight  very  severe  shocks,  each  of 
which  did  great  damage  and  spread  devastation  far  and  wide. 

3.  The  eye-witnesses  generally  agree  that  these  severe  shocks 
were  preceded  by  heavy  subterranean  thunder ;   "  a  loud   roaring 
sound  like  steam  escaping  from  a  boiler  " ;  "  distant  rumbling  sounds 
succeeded  by  discharges  as  if  a  thousand  pieces  of  artillery  were 


i9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  389 

suddenly  exploded  " ;  "a  rumbling  like  distant  thunder  " ;  "  an  aw- 
ful noise  resembling  loud  and  distant  thunder,  but  more  hoarse 
and  vibrating,"  are  some  of  the  descriptions. 

4.  All  the  severe   shocks  were  accompanied  by  the  escape  of 
sulphurous   vapors   from   the  great   fissures   which   opened   in   the 
earth;  and  on  December  16,  after  7  a.  m.,  the  severe  shock  was 
accompanied  by  total  darkness  till  sunrise ;  in  one  of  the  shocks 
witnessed  by  J.  J.  Audubon  near  Henderson,  Kentucky,  he  took 
the  cloud  of  vapor  on  the  western  horizon  for  a  rising  storm;  and 
in  general  the  eye-witnesses  in  Missouri  agree  that  flashes  were 
frequently   observed   as   if   these   vapors   were   generating   electric 
discharges  in  the  air. 

5.  The  severe  earthquake  shock  of  February  7,  1812,  lasted  four 
minutes,  according  to  Jarred  Brooks  of  Louisville,  Kentucky,  who 
seems   to   have   given   much   attention   to   these   phenomena,    and 
classified  them  carefully.     He  said :  "  It  seemed  as  if  the  surface  of 
the  earth  was  afloat  and  set  in  motion  by  a  slight  application  of  im- 
mense  power,   then   a   boiling   action   succeeded,   houses   oscillate, 
gables  and  chimneys  of  many  houses  are  thrown  down." 

6.  Great  fissures  running  nearly  north  and  south  (Lyell's  meas- 
urement in  1846  made  the  direction  from  10°  to  45°  W.  of  N.)  were 
formed  five  miles  long,  ten  feet  wide,  and  four  feet  deep,  by  the 
great  undulations  which  came  from  the  west ;  hills  were  sunk,  forests 
inundated,  lakes  drained,  swamps  formed,  the  bed  of  the  Mississippi 
River  upheaved  so  that  its  waters  backed  up  for  a  time,  then  came 
booming  on,  broke  over  and  swept  everything  before  them,  and 
nearly  all  the  shipping  was  destroyed;  hills  rose  where  lakes  and 
swamps  formerly  stood;  the  waters  of  the  Mississippi  receded  from 
its  banks  and  then  returned  as  a  wall  fifteen  or  twenty  feet  high, 
tearing  the  boats   from  their  moorings   and  carrying  them  up  a 
creek  a  quarter  of  a  mile. 

7.  Water  and  sand,  and  some  coal  or  lignite,  and  sulphur  was 
ejected   from  the  fissures,   the  materials  being  thrown   forty   feet 
high,  which  aided  in  filling  the  air  with  noxious  vapors. 

The  ejection  of  this  material  from  the  ground  would  explain 
some  of  the  noises  which  accompanied  these  earthquakes,  but  not 
all.  The  deep  subterranean  thunder  preceding  the  shocks  cannot 


390  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

be  explained  except  by  explosions  in  the  earth.  Some  of  the  land 
was  'no  doubt  simply  settled  by  shaking,  but  this  will  not  account  for 
the  upheaval  of  the  bed  of  the  Mississippi  River  so  as  to  make  its 
waters  flow  upstream ;  and  we  seem  obliged  to  admit  that  in  addition 
to  subsidence  there  was  also  elevation  of  ground. 

The  New  Madrid  earthquake  is  extremely  remarkable  for  its  nu- 
merous severe  shocks  and  the  long  intervals  at  which  they  occurred, 
the  last  great  shock  of  February  7,  1812,  being  the  worst  of  all.  The 
order  of  events  does  not  harmonize  so  well  in  the  tectonic  theory  of 
rock  slipping  as  it  does  with  Strabo's  account  of  a  volcanic  out- 
break near  Chalcis,  in  Euboea,  in  which  the  shocks  ceased  only 
after  a  fissure  opened  on  the  Lelantine  Plain  and  ejected  a  fiery 
river  of  mud.  To  be  sure,  no  lava  was  ejected  in  the  New  Madrid 
earthquake,  but  the  phenomena  resemble  those  described  by  Strabo, 
in  which  elastic  vapors  within  the  earth  were  seeking  release.  If 
no  single  outburst  of  lava  and  steam  could  break  forth  above  ground 
the  agitation  might  on  that  account  continue  all  the  longer,  and  an 
impartial  study  of  this  remarkable  earthquake  strongly  suggests 
this  explanation.  The  whole  course  of  events  is  singularly  incon- 
sistent with  any  suggestion  that  mere  slipping  of  rock  or  subsidence 
was  involved. 

We  have  examined  this  earthquake  in  detail,  because  it  is  little 
understood  and  so  complex  and  extraordinary  in  respect  to  location 
and  duration  that  it  constitutes  a  severe  test  of  any  theory ;  and  yet 
a  comprehensive  theory  must  be  able  to  account  for  such  phenomena 
without  prejudice  to  the  historical  facts. 

§  53.  Other  important  earthquakes. 

»If  we  examine  attentively  the  available  details  of  various  other 
earthquakes  which  are  classed  as  tectonic  we  shall  find  that  most 
if  not  all  of  them  give  evidence  of  high  explosive  power  within 
the  earth.  Under  ordinary  conditions  it  may  be  supposed  that  these 
forces  are  exerted  long  enough  to  afford  partial  or  complete  release 
from  the  strain,  and  then  the  agitation  ceases  or  continues  in  the 
form  of  slight  after-shocks.  It  is  only  when  unlifts  occur  that 
we  have  direct  proof  of  an  uplifting  force,  the  visible  effect  of 
subterranean  explosive  power;  but  it  would  seem  that  the  heaving 
of  the  earth  accompanying  the  rending  of  strata  and  breaking  of 


X9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  391 

rocks  is  a  fairly  obvious  indication  of  imprisoned  vapors  seeking 
release  from  contact  with  molten  rock. 

In  fact  nearly  all  the  -  recent  important  earthquakes  of  great 
violence,  and  inappropriately  classed  as  tectonic,  present  strong 
indications  of  being  due  to  steam  power.  It  probably  is  not  too 
much  to  say  that  it  is  doubtful  if  one  of  them  could  be  fairly  ex- 
plained by  mere  subsidence  due  to  the  slipping  of  rock  faults. 

In  almost  every  case  it  will  be  found  that  the  rock  slipping 
noted  at  the  surface  is  small,  while  it  is  conceded  that  the  chief 
effect  must  depend  upon  great  forces  exerted  from  deep  down.  This 
seems  to  be  substantially  admitted  by  most  writers,  who  have  a  sus- 
picion that  the  forces  are  singularly  deep-seated  and  otherwise  act 
in  a  strange  way.  The  Charleston  earthquake  originated  twelve 
miles  below  the  surface,  while  the  San  Francisco  earthquake  will 
not  prove  to  be  of  less  depth.  The  Bengal-Assam  earthquake  of 
June  12,  1897,  investigated  by  Mr.  R.  D.  Oldham,  must  have  had 
great  depth,  owing  to  the  wide  extent  of  country  over  which  is  was 
felt  and  the  great  intensity  of  the  shocks.  The  same  is  true  of  the 
Mino-Owari  earthquake  of  October  18,  1891,  and  all  other  earth- 
quakes of  high  intensity  which  were  widely  felt.  The  Valparaiso 
earthquake  of  August  16,  1906,  was  among  the  most  terrible  of 
modern  times,  and  it  was  so  widely  felt  that  the  depth  could  hardly 
be  less  than  fifteen  or  twenty  miles. 

It  seems  desirable  to  direct  attention  to  the  fact  that  probably 
not  one  of  these  great  earthquakes  has  occurred  in  a  region  where 
seeping  of  water  and  formation  of  steam  may  not  have  been  the 
dynamic  cause.  The  center  of  the  violent  Bengal-Assam  earthquake 
was  under  the  great  Bramaputra  River,  where  it  spreads  to  great 
width  and  drains  an  immense  volume  of  water  from  the  Himalayas. 
This  region  was  originally  a  deep  trough  in  the  sea  and  has  since 
been  filled  in ;  and  owing  to  the  great  surface  drainage  is  still 
essentially  an  inland  sea  not  far  from  the  Bay  of  Bengal,  which 
receives  also  the  Ganges  as  well  as  the  Bramaputra.  The  situation 
is  very  similar  to  that  of  New  Madrid,  but  is  nearer  the  sea,  and 
has  the  Himalayas  on  the  north,  from  which  the  drainage  is  enor- 
mous. Besides  there  is  in  that  region  a  natural  survival  of  the  forces 
which  uplifted  the  Himalayas,  and  this  ancient  sea  valley  did  most 
of  the  work  involved  in  the  raising  of  these  mighty  mountains. 

PROC.  AMER.   PHIL.  SOC.,  XLV.    184  Y,  PRINTED  FEBRUARY  25,   1907. 


392  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

If  we  examine  the  violent  Japanese  earthquakes  we  shall  find 
that  most  of  them,  as  Professor  Milne  says,  arise  under  the  sea  near 
the  seashore  or  at  the  heads  of  bays,  where  the  influence  of  the  sea 
would  predominate.  .It  seems  impossible  to  doubt  that  they  are  due 
to  the  influence  of  steam  formed  in  the  earth  beneath ;  for  the  island 
of  Nipon  is  essentially  narrow,  mountainous  and  broken  by  great 
irregularity  of  topography,  so  that  the  seepage  of  water  is  easily 
accounted  for,  and  more  especially  since  the  worst  earthquakes  are 
on  the  east  coast  and  partly  under  the  sea  on  the  edge  of  the  Tus- 
carora  Deep,  where  the  shore  is  steepest  and  the  sea  pressure 
greatest.  Moreover,  it-4s"Shown  in-~§  -^^-that  the  whole  island  of 
Nipon  has  been  uplifted  by  injections  of  matter  expelled  largely 
from  under  the  bed  of  the  Tuscarora  Deep ;  and  what  is  more  natT 
ural  than  to  suppose  that  this  process  is  still  going  on  ?  This  infer- 
ence in  fact  is  confirmed  by  the  secular  elevation  of  the  east  coast 
observed  within  the  historical  period. 

The  regions  of  Iberian  Peninsula  visited  by  violent  earthquakes 
are  those  similarly  exposed  to  the  sea — Lisbon  and  the  southern  prov- 
inces, such  as  Andalusia,  which  are  also  broken  and  mountainous,  and 
have  been  recently  rising  from  the  sea.  In  Italy  the  region  of  great- 
est and  most  violent  disturbance  is  Calabria,  the  "  toe  of  the  boot," 
which  is  a  long  peninsula  nearly  surrounded  by  the  sea  and  of  re- 
markably fractured  and  broken  topography.  The  islands  of  Sicily, 
Ischia,  Lapari,  Stromboli  and  the  coast  near  Vesuvius  is  similar, 
and  all  these  regions  are  still  rising  from  the  sea.  Nearly  all  Greece 
is  very  broken  and  mountainous  and  it  has  always  suffered  severely 
from  earthquakes.  In  Hungary,  where  the  severe  earthquake  of 
Agram,  Croatia,  occurred  November  9,  1880,  the  country  is  full  of 
hot  springs,  indicating  an  abundance  of  underground  water,  and 
while  the  volcanoes  have  died  out  the  earthquakes  still  survive.  The 
earthquake  in  Silesia,  June  n,  1895,  occurred  in  a  region  of  the 
same  kind. 

If  now  we  turn  to  Central  America  we  find  it  a  narrow  broken 
country  with  sea  on  both  sides ;  and  on  the  other  side  of  the  Pacific, 
New  Zealand  is  a  narrow  island  like  Japan,  and  the  presence  of 
violent  earthquakes  there  is  not  strange.  The  same  may  be  said 
of  the  Aleutian  Islands  and  the  whole  East  Indian  Archipelago, 
including  the  Philippines. 


I90.6]  SEE— THE  CAUSE  OF  EARTHQUAKES.  393 

The  same  reasoning  applies  to  all  the  South  American  earth- 
quakes, including  those  which  have  destroyed  Caracas,  Cumana,  and 
other  places  in  Venezuela.  This  coast  lies  between  the  eastern  spur 
of  the  Andes  and  the  waters  of  the  Caribbean  Sea,  which  is  one 
of  the  deepest  parts  of  the  Atlantic,  and  the  intensity  of  the  sub- 
terranean forces  is  shown  by  the  violence  of  the  volcanic  outbreaks 
in  the  Lesser  Antilles. 

_J  54.  Are  any  earthquakes  really  tectonic? 

\It  is  held  that  many  earthquakes  are  tectonic  because  there  is 
externally  only  a  movement  of  the  strata,  as  if  they  were  seeking 
release  from  strain,  and  obvious  volcanic  forces  do  not  appear. 
Boussingault  long  ago  concluded  that  many  of  the  earthquakes  in 
the  Andes  depended  on  the  settling  of  the  strata  in  these  mountains, 
and  this  was  the  beginning  of  the  tectonic  theory  that  most  earth- 
quakes are  due  to  collapse  or  movement  for  release  of  strain.  To 
test  the  validity  of  this  theory,  it  is  advisable  to  apply  similar  reason- 
ing to  the  mountains  of  a  country  remote  from  the  seacoast.  We 
choose  for  this  purpose  the  Rocky  Mountains  in  Colorado,  which 
were  formerly  near  but  are  now  remote  from  the  sea.  If  what 
Boussingault  witnessed  in  the  Andes  was  really  the  settling  of  the 
mountains,  the  same  effects  ought  to  be  going  on  in  the  Rocky 
Mountains  of  Colorado.  So  far  as  the  records  of  history  go,  it  may 
be  safely  said  that  not  a  single  serious  earthquake  has  ever  visited 
Colorado,  and  yet  many  should  have  been  felt  if  Boussingault's 
theory  of  the  settling  of  the  mountains  is  correct.  As  change  is 
usually  ascribed  to  secular  cooling,  why  should  the  Andes  settle 
and  not  the  Rocky  Mountains?  From  the  absence  of  earthquakes 
in  Colorado,  it  is  evident  that  tectonic  movements  have  ceased  in 
that  region,  though  secular  cooling  has  not;  and  thus  we  see  that 
these  movements  after  all  do  not  depend  on  settlement  of  the  moun- 
tains due  to  the  shrinkage  of  the  earth.  For,  if  so,  it  is  incredible 
that  the  Rocky  Mountains  can  have  already  attained  a  perfectly 
stable  position.  They  ought  to  be  still  collapsing  like  the  Andes, 
since  secular  cooling  is  always  going  on.  Thus  we  see  that  all 
earthquakes  must  depend  on  underlying  explosive  forces,  and  not 
on  mere  adjustments  of  strata  to  secure  release  of  strain  or  stability 
of  position,  required  by  the  progress  of  secular  cooling^j 


394  SEE-THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

Another  way  to  reach  this  result  is  to  recall  that  the  investiga- 
tion of  earthquakes  in  Hungary,  Croatia,  Bohemia  and  other  coun- 
tries shows  that  most  frequently  the  impulse  proceeds  from  an 
underlying  area  of  considerable  extent,  and  not  from  a  point  nor 
line,  though  the  surface  movement  may  be  chiefly  along  the  nearest 
fault.  If  the  underlying  area  from  which  the  shock  proceeds  is 
elliptical,  as  usually  happens,  we  may  be  quite  sure  that  this  diffusion 
of  the  impulse  over  an  area  indicates  an  underlying  outspread  sheet 
of  lava  saturated  with  steam,  which  finally  acquires  such  tension  that 
it  is  enabled  to  shake  the  overlying  crust  and  cause  a  movement 
along  the  fault  lines  where  the  crust  is  broken  and  movement  is 
easiest.  The  lava  sheet  seeks  readjustment,  and  in  the  process  of 
equalizing  the  strain,  movement  of  the  molten  rock  takes  place,  and 
the  faults  not  only  move  vertically,  but  often  also  horizontally. 
This  is  a  natural  and  simple  explanation  of  fault  movement,  and  it 
accounts  for  the  rotatory  motion  so  frequently  noticed  in  earth- 
quakes. The  great  earthquakes  of  Lisbon,  Arica  and  Iquique  have 
usually  been  classed  as  tectonic,  but  in  view  of  the  sinking  of  the 
bed  of  the  sea  shown  by  the  accompanying  seismic  sea  waves,  it  is 
clear  that  all  these  terrible  disturbances  were  due  to  the  expulsion 
of  lava  from  under  the  ocean. 

§  55.  The  geological  significance  of  earthquakes. 

In  their  new  work  on  "  Geology  "  (Vol.  I,  p.  534)  Chamberlin 
and  Salisbury  remark  that  "  Earthquakes  are  of  much  less  im- 
portance, geologically,  than  many  gentler  movements  and  activities. 
Disastrous  as  they  sometimes  are  to  human  affairs,  they  leave  few 
distinct  and  readily  identifiable  marks  which  are  more  than  tem- 
porary." Mention  is  made  of  the  effects  of  earthquakes  in  fractur- 
ing the  rocks  of  the  earth's  crust,  but  the  fractures,  it  is  pointed  out, 
do  not  show  at  the  surface  when  the  soil  is  deep.  These  authors 
also  remark  (p.  527)  that  "  the  most  prevalent  (source  of  earth- 
quakes) is  probably  the  fracture  of  rocks  and  the  slipping  of  strata 
on  each  other  in  the  process  of  faulting." 

Let  us  now  examine  these  remarks  a  little  more  carefully.  If 
earthquakes  are  due  to  fracture  of  rocks  and  the  slipping  of  strata, 
it  follows  that  the  forces  involved  here  have  played  no  part  in  the 
original  formation  of  the  globe,  but  are  the  effects  of  collapse  after 


19o6.)  SEE— THE  CAUSE  OF  EARTHQUAKES.  395 

the  mountains  were  formed.  On  this  view,  earthquakes  would  be 
of  very  small  consequence  geologically,  because  they  are  associated 
only  with  destructive  and  not  with  constructive  processes.  But  is 
such  a  view  tenable  ?  If  earthquakes  are  not  due  to  the  same  forces 
which  upheaved  the  mountains,  what  other  forces  besides  these  have 
been  active  in  the  development  of  the  globe?  The  only  forces  of 
construction  now  felt  upon  the  earth  are  those  exerted  in  earth- 
quakes. So  far  as  we  can  see,  no  other  constructive  forces  are  at 
work.  Therefore,  the  forces  felt  in  earthquakes  are  identical  with 
those  which  formed  the  mountains,  and  this  is  sometimes  admitted, 
though  mountain  formation  itself  is  assigned  to  the  wrong  cause. 

Destructive  forces  such  as  erosion  are  wearing  down  the  struc- 
ture of  the  globe,  while  earthquakes  are  the  only  known  forces  which 
are  building  it  up.  We  take  it,  therefore,  that  so  far  from  being  of 
little  importance  geologically  the  forces  felt  in  earthquakes  are  of 
the  greatest  importance,  and  most  of  the  constructive  forces  'in  the 
development  of  the  earth  are  due  to  this  cause.  The  destructive 
effects  of  earthquakes  are  only  incidental  to  the  more  fundamental 
constructive  purpose  which  underlies  the  operation  of  these  forces. 
When  an  earthquake  occurs  rocks  in  unstable  positions  fall,  loose 
sediment  is  shaken  down,  and  other  settlements  occur,  but  the  real 
constructive  work  consists  in  upheavals,  little  by  little  it  may  be, 
of  mountains,  islands,  coasts,  plateaus  and  larger  areas.  These 
elevations  are  actually  witnessed  in  certain  earthquakes,  and  could 
not  possibly  arise  from  any  processes  of  collapse.  Sometimes  these 
constructive  forces  work  slowly  and  quietly,  but  usually  with  more 
or  less  violence;  and  the  usual  method  of  elevation  is  by  the  injec- 
tion of  lava  saturated  with  steam. 

What  has  been  taken  to  be  the  cause  of  earthquakes,  namely, 
the  slipping  of  rocks,  is  really  the  effects  of  more  deep-seated  ex- 
plosive forces.  Earthquakes,  therefore,  are  not  due  to  the  effects 
of  secular  cooling,  but  to  the  vapor  of  steam  arising  from  the  pene- 
tration of  water  into  the  heated  layers  just  beneath  the  crust.  If 
earthquakes  were  due  to  cooling  they  ought  to  be  as  frequent  in 
desert  regions  as  in  deep  seas  along  the  shores  of  continents,  where 
they  really  are  abundant. 


396  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

XL     EARTH  TREMORS  AND  TELESEISMIC  DISTURBANCES. 

§  56.  Slight  movements  of  the  earth. 

A  great  many  questions  recently  have  been  discussed  relating  to 
slight  slow  oscillations  shown  by  horizontal  pendulums  and  other 
instruments  designed  to  detect  delicate  changes  of  level.  No  doubt 
very  many  of  these  changes  are  correctly  ascribed  to  the  yielding 
of  the  solid  earth,  due  to  variable  loading  of  the  soil  by  tidal,  sea- 
sonal and  meteorological  influences.  But  may  not  others  be  due 
to  the  slow  but  steadily  varying  influence  of  subterranean  forces 
as  discussed  in  this  paper?  Some  of  the  strains  thus  constantly 
arising  would  be  released  by  microseismic  disturbances  which  show 
no  periodicity'  or  regularity ;  while  others  would  be  cumulative  and 
have  at  length  a  small  secular  effect.  The  fact  that  the  ground  in 
most  places  is  comparatively  so  stable  under  the  test  of  astronomical 
observations  seems  to  show  that  these  effects  usually  are  slight, 
-except  in  the  neighborhood  of  the  sea ;  but  many  small  irregular 
disturbances  occur,  and  it  is  not  improbable  that  a  considerable 
number  of  them  may  have  their  origin  hidden  deeper  in  the  earth 
than  heretofore  has  been  suspected.  If  great  earthquakes  originate 
.at  depths  of  from  eight  to  twenty  miles,  we  may  be  sure  that  the 
forces  there  at  work  produce  some  surface  changes  of  level  even  if 
mo  violent  outbreaks  occur. 

§  57.  Humboldt' s  views  on  earthquakes. 

Jn  the  fifth  volume  of  the  Cosmos  (p.  288)  Humboldt  justly 
remarks  how  Charles  Darwin,  "  with  his  peculiar  generalizing  view, 
has  grasped  the  connection  of  the  phenomena  of  earthquakes  and 
eruptions  of  volcanoes  under  one  point  of  view." 

In  his  "Views  of  Nature,"  Vol.  I,  p.  361,  Humboldt  alludes  to 
the  nearly  simultaneous  occurrence  of  volcanic  and  seismic  phe- 
nomena in  places  widely  separated,  and  says : 

"  All  these  phenomena  prove  that  subterranean  forces  are  manifested 
either  dynamically,  explosively,  and  attended  by  commotion,  in  earthquakes; 
or  possess  the  property  of  producing,  or  of  chemically  modifying  a  substance 
in  volcanoes;  and  they  further  show,  that  these  forces  are  not  seated  near 
.  the  surface  in  the  thin  crust  of  the  earth,  but  deep  in  the  interior  of  our 
planet,  whence  through  fissures  and  unfilled  veins  they  act  simultaneously  at 
widely  distant  points  of  the  earth's  surface." 

And  in  his  "  Travels,"  Vol.  I,  p.  172-3,  he  adds: 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  397 

"  Everything  in  earthquakes  seems  to  indicate  the  action  of  elastic  fluids 
seeking  an  outlet  to  diffuse  themselves  in  the  atmosphere.  Often  on  the 
coasts  of  the  Pacific,  the  action  is  almost  simultaneously  communicated  from 
Chili  to  the  Gulf  of  Guayaquil,  a  distance  of  six  hundred  leagues;  and,  what 
is  very  remarkable,  the  shocks  appear  to  be  the  stronger  in  proportion  as 
the  country  is  more  distant  from  burning  volcanoes.  The  granitic  mountains 
of  Calabria,  covered  with  very  recent  breccias,  the  calcareous  chain  of  the 
Apennines,  the  country  of  Pignerol,  the  coasts  of  Portugal  and  Greece,  those 
of  Peru  and  Terra  Firma,  afford  striking  proofs  of  this  fact.  The  globe,  it 
may  be  said,  is  agitated  with  the  greater  force,  in  proportion  as  the  surface 
has  a  smaller  number  of  channels  communicating  with  the  caverns  of  the 
interior.  At  Naples  and  at  Messina,  at  the  foot  of  Cotopaxi  and  of  Tun- 
guragua,  earthquakes  are  dreaded  only  when  vapor  and  flames  do  not  issue 
from  the  craters.  In  the  kingdom  of  Quito,  the  great  catastrophe  of  Riobamba 
led  several  well-informed  persons  to  think  that  that  country  would  be  less 
frequently  disturbed,  if  the  subterranean  fire  should  break  the  porphyritic 
dome  of  Chimborazo;  and  if  that  colossal  mountain  should  become  a  burning 
volcano.  At  all  times  analogous  facts  have  led  to  the  same  hypotheses. 
The  Greeks,  who  like  ourselves,  attributed  the  oscillations  of  the  ground  to 
the  tension  of  elastic  fluids,  cited  in  favour  of  their  opinion,  the  total  cessa- 
tion of  the  shocks  at  the  island  of  Eubcea,  by  the  opening  of  a  crevice  in  the 
Lelantine  plain."1 

§  58.  Views  of  Charles  Darwin. 

In  the  "  Voyage  of  a  Naturalist,"  Chapter  xiv,  Darwin  says : 

"  The  forces  which  slowly  and  by  little  starts  uplift  continents,  and 
those  which  at  successive  periods  pour  forth  volcanic  matter  from  open 
orifices,  are  identical.  For  many  reasons,  I  believe  that  the  frequent  quak- 
ings  of  the  earth  on  this  line  of  coast  (Chili)  are  caused  by  the  rending  of 
the  strata,  necessarily  consequent  on  the  tension  of  the  land  when  upraised, 
and  their  injection  by  fluidified  rock.  I  believe  that  the  solid  axis  of  a  moun- 
tain differs  in  its  manner  of  formation  from  a  volcanic  hill,  only  in  the 
molten  stone  having  been  repeatedly  injected,  instead  of  having  been  re- 
peatedly ejected. 

"Moreover,  I  believe  that  it  is  impossible  to  explain  the  structure  of 
great  mountain-chains,  such  as  that  of  the  Cordillera,  where  the  strata, 
capping  the  injected  axis  of  plutonic  rock,  have  been  thrown  on  their  edges 
along  several  parallel  and  neighboring  lines  of  elevation,  except  on  this 
view  of  the  rock  of  the  axis  having  been  repeatedly  injected,  after  intervals 
sufficiently  long  to  allow  the  upper  parts  or  wedges  to  cool  and  become  solid ; 
— for  if  the  strata  had  been  thrown  into  their  present  highly  inclined,  vertical, 
and  even  inverted  positions,  by  a  single  blow,  the  very  bowels  of  the  earth 
would  have  gushed  out;  and  instead  of  beholding  abrupt  mountain  axes  of 
rock  solidified  under  great  pressure,  deluges  of  lava  would  have  flowed  out 
at  innumerable  points  of  every  line." 

"The  shocks  ceased  only  when  a  crevice,  which  ejected  a  river  of  fiery 
mud,  opened  in  the  plain  of  Lelantum,  near  Chalcis." — Strabo. 


398  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

This  view  of  mountain  formation  is  essentially  identical  with 
that  here  adopted,  except  that  I  conceive  the  interior  part  of  a 
mountain,  whether  a  peak  or  a  chain,  to  be  filled  underneath  with 
porous  lava,  which  explains  the  feebleness  of  the  attraction  of 
mountains  and  the  readiness  with  which  they  are  converted  into 
volcanoes  when  once  their  tops  are  burst  open  during  the  paroxysms 
of  an  earthquake.  The  present  views  therefore  confirm  and  some- 
what extend  those  Held  by  the  elder  Darwin  seventy  years  ago.  In 
Chapter  VI  of  his  "  Geological  Observations  on  Volcanic  Islands  " 
the  great  naturalist  says : 

"  Some  authors  have  remarked  that  volcanic  islands  occur  scattered, 
though  at  very  unequal  distances,  along  the  shores  of  the  great  continents, 
as  if  in  some  measure  connected  with  them.  In  the  case  of  Juan  Fernandez, 
situated  330  miles  from  the  coast  of  Chile,  there  was  undoubtedly  a  con- 
nection between  the  volcanic  forces  acting  under  this  island  and  under  the 
continent,  as  was  shown  during  the  earthquake  of  1835.  The  islands,  more- 
over, of  some  of  the  small  volcanic  groups  which  thus  border  continents, 
are  placed  in  lines,  related  to  those  along  which  the  adjoining  shores  of  the 
continents  trend;  I  may  instance  the  lines  of  intersection  at  the  Galapagos, 
and  at  the  Cape  de  Verde  Archipelagoes,  and  the  best  marked  line  of  the 
Canary  Islands.  If  these  facts  are  not  merely  accidental,  we  see  that  many 
scattered  volcanic  islands  and  small  groups  are  related  not  only  by  proximity, 
but  in  the  direction  of  the  fissures  of  eruption  to  the  neighboring  continents 
— a  relation  which  Von  Buch  considers  characteristic  of  his  great  volcanic 
chains. 

"  We  ought  not,  however,  to  suppose,  in  hardly  any  instance,  that  the 
whole  body  of  matter,  forming  a  volcanic  island,  has  been  erupted  at  the 
level  on  which  it  now  stands ;  the  number  of  dikes,  which  seem  invariably  to 
intersect  the  interior  parts  of  every  volcano,  show,  on  the  principles  of  M. 
Elie  de  Beaumont,  that  the  whole  mass  has  been  uplifted  and  fissured.  A 
connection,  moreover,  between  volcanic  eruptions  and  contemporaneous  ele- 
vations in  mass1  has,  I  think,  been  shown  to  exist  in  my  work  on  Coral 
Reefs,  both  from  the  frequent  presence  of  upraised  oreanic  remains  and 
from  the  structure  of  the  accompanying  coral  reefs.  Finally,  I  may  remark, 
that  in  the  same  Archipelago  (Galagapos),  eruptions  have  taken  place  within 
the  historical  period  on  more  than  one  of  the  parallel  lines  of  fissure:  thus, 
at  the  Galapagos  Archipelago  eruptions  have  taken  place  from  a  vent  on 
Narborough  Island,  and  from  one  on  Albemarle  Island,  which  vents  do  not 
fall  on  the  same  line;  at  the  Canary  Islands,  eruptions  have  taken  place  in 
Teneriffe  and  Lanzarote;  and  at  the  Azores,  on  the  three  parallel  lines  of 
Pico,  St.  Jorge,  and  Terciera.  Believing  that  a  mountain  axis  differs  essen- 

1 A  similar  conclusion  is  forced  on  us  by  the  phenomena  which  accom- 
panied the  earthquake  of  1835,  at  Conception,  and  which  are  detailed  in  my 
paper  (Vol.  V,  p.  601)  in  the  Geological  Transactions. 


I906.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  399 

tially  from  a  volcano,  only  in  pultonic  rocks  having  been  injected,  instead  of 
volcanic  matter  having  been  ejected,  this  appears  to  me  an  interesting  circum- 
stance; for  we  may  infer  from  it  as  provable,  that  in  the  elevation  of  a 
mountain  chain,  two  or  more  of  the  parallel  lines  forming  it  may  be  upraised 
and  injected  within  the  same  geological  period." 

§  59-  Views  of  Professor  Milne. 

Professor  Milne  has  recently  expressed  views  of  somewhat 
similar  character,  many  of  which  agree  closely  with  those  reached  in 
this  paper.  In  the  recent  Bakerian  Lecture  before  the  Royal  Society, 
he  says: 

"  But  if,  instead  of  confining  our  attention  to  a  relationship  between 
earthquakes,  we  consider  the  question  of  the  relief  of  volcanic  strain,  many 
illustrations  may  be  adduced  which  indicate  a  close  connection  between  such 
activities.  For  example,  all  the  known  volcanic  eruptions  which  have  oc- 
curred in  the  Antilles,  from  the  first  which  took  place  in  1692,  have  been 
heralded  or  closely  accompanied  by  large  earthquakes  in  that  region,  but 
more  frequently  by  like  disturbances  in  neighboring  rock-folds,  particularly 
that  of  the  Cordilleras.  This  was  notably  the  case  in  1902.  On  April  19 
of  that  year  an  unusually  large  earthquake  devastated  cities  in  Guatemala. 
Small  local  shocks  were  felt  in  the  West  Indies,  and  on  April  25  it  was  no- 
ticed that  steam  was  escaping  from  the  crater  on  Mont  Pelee,  in  Martinique. 
These  activities  continued  to  increase  until  May  8,  when  they  terminated 
with  terrific  explosions,  submarine  disturbances,  and  the  devastation  of  great 
portions  of  the  islands  of  Martinique  and 'St.  Vincent. 

"  The  last  illustration  of  hypogene  relationship  between  these  regions 
occurred  on  Januarv  31  of  the  present  year.  On  that  date  a  heavy  earth- 
quake originated  off  the  mouth  of  the  Esmeralda  River,  in  Columbia.  Sea- 
waves  inundated  the  coast,  islands  sank,  and  a  volcano  erupted.  The  news- 
papers of  February  2  announced  that  cables  between  Jamaica  and  Puerto 
Rico  had  been  interrupted,  and  on  later  dates  it  was  reported  that  severe 
shocks  had  been  felt  among  the  West  Indian  islands,  that  six  or  seven  sub- 
marine cables  had  been  broken,  and  that  Mont  Pelee  and  La  Soufriere,  in 
St.  Vincent,  were  again  active."  * 

We  have  quoted  these  views  of  Humboldt,  Darwin  and  Milne 
in  order  to  exhibit  fairly  the  beliefs  of  all  these  great  investigators 
in  the  development  or  the  possibility  of  the  development  of  seismic 
action  at  a  distance  when  a  disturbance  is  once  started. 
§  60.  Tele  seismic  disturbances. 

From  the  theory  developed  in  this  paper  we  take  is  that  when  a 

severe  earthquake  is  started  at  one  place  the  tremors  may  cause 

disturbances  to  spread  into  neighboring  regions  or  to  break  out  at 

a  distant  point  if  the  conditions  of  the  steam  pressure  underlying 

1  Proc.  Roy.  Soc.,  Vol.  77,  1906,  p.  374. 


400  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  i9( 

the  crust  are  already  highly  unstable ;  but  there  is  probably  no  com- 
munication through  the  depths  of  the  planet,  except  a  wave  motion 
which  spreads  in  every  direction,  the  earth  acting  as  an  aeolotropic 
elastic  solid,  because  of  the  great  pressure  to  which  the  matter  is 
subjected.  In  adopting  the  view  that,  because  sympathetic  effects 
may  be  aroused  at  great  distances,  the  disturbances  are  therefore 
very  deep-seated,  Humboldt  appears  to  have  been  somewhat  misled 
by  the  ordinary  effects  of  tremors  on  unstable  conditions  even  at 
great  distances. 

Yet  there  can  scarcely  be  any  doubt  that  the  connection  of  the 
Andean  trough  from  Valdivia  to  Guayaquil  is  so  intimate  that  a  dis- 
turbance once  started  under  parts  of  it  may  easily  be  propagated 
over  the  whole  length  of  this  great  trough,  or  even  to  another  part 
of  the  globe;  and  thus  we  conclude  that  seismic  activity  easily 
extends,  and  has  a  widespread  effect  which  was  formerly  supposed 
to  be  transmitted  through  the  deep  interior  of  the  earth.  It  is 
impossible  to  doubt  that  Charles  Darwin  was  entirely  correct  in 
concluding  that  a  subterranean  connection  generally  exists  between 
a  continent  and  its  outlying  islands,  for  both  are  often  on  the 
borders  of  the  same  continental  trough.  Occasionally  the  extent 
of  this  connection  may  be  even  wider,  and  sometimes  cover  a  whole 
region  or  run  from  one  region  into  another,  as  in  the  events  men- 
tioned above  by  Professor  Milne ;  but  the  disturbances  are  trans- 
mitted principally  by  waves  and  by  strains  through  the  crust,  and 
not  by  means  of  any  currents  through  the  deep  interior  of  the  earth. 
As  regards  the  general  question  of  slight  disturbances  bringing  on 
greater  catastrophes  when  the  conditions  of  subterranean  steam 
pressure  are  already  highly  unstable  we  may  go  even  further.  We 
occasionally  read  in  History  of  the  West  Indies,  especially  the 
group  including  St.  Vincent,  Martinique,  St.  Lucia,  Guadaloupe, 
Barbadoes  and  Trinidad,  being  visited  by  a  terrible  hurricane,  fol- 
lowed by  an  earthquake  and  a  "  tidal  wave  " ;  so  that  it  seems  as 
if  all  the  worst  elements  in  nature  were  suddenly  let  loose  to  devas- 
tate these  islands.  In  view  of  the  cause  assigned  in  this  paper,  it 
is  evident  that  unstable  conditions  of  subterranean  steam  pressure 
may  not  require  anything  more  violent  than  the  raging  of  a  hurri- 
cane to  bring  on  an  earthquake,  which  in  turn  may  be  followed 


Jgo6  j  SEE— THE  CAUSE  OF  EARTHQUAKES.  401 

by  a  "  tidal  wave,"  for  the  reasons  and  in  the  manner  above  ex- 
plained; and  thus  to  the  afflicted  inhabitants  all  nature  seems  to  be 
convulsed  at  once.  From  the  observed  course  of  events,  we  cannot 
doubt  that  this  connection  actually  exists ;  and  unfortunately  it 
seems  to  be  abundantly  illustrated  in  the  annals  of  the  East  as  well 
as  of  the  West  Indies. 

In  the  same  way  we  explain  Alexis  Perrey's  well-known  laws 
of  earthquakes.  The  forces  assigned  to  account  for  these  disturb- 
ances, however,  are  not  the  cause  of  the  convulsions  of  nature,  but 
only  the  occasions  for  outbreaks  of  highly  unstable  conditions  de- 
pending on  subterranean  forces  easily  set  off. 

In  like  manner  the  violent  outbreak  of  a  volcano  or  the  occur- 
rence of  a  great  earthquake  in  one  part  of  the  world  may  tend  to 
bring  on  similar  phenomena  in  another  remote  region. 

The  order  of  events  often  observed  in  the  development  of  the 
volcanic  and  seismic  phenomena  following  great  outbreaks  seems 
to  support  this  view.  While  we  do  not  regard  it  as  proved  that 
an  eruption  like  the  recent  great  outbreak  of  Vesuvius,  for  example, 
could  indirectly  bring  on  the  earthquake  in  California  and  other 
similar  disturbances,  yet  we  do  not  regard  such  an  influence  as 
at  all  impossible.  Conditions  of  instability  once  existing  are  con- 
tagious and  tend  to  spread  like  a  conflagration.  As  there  are  on 
the  average  over  60  world-shaking  earthquakes  every  year,  or 
more  than  one  a  week,  it  is  evident  that  if  one  should  break  out  in 
a  region  where  it  might  accelerate  the  outbreak  of  others,  several 
might  be  grouped  into  a  small  space  of  time,  and  these  in  turn  might 
exercise  wide  influence  on  unstable  conditions  throughout  the  world, 
as  often  seems  to  be  the  case.1  Our  knowledge  of  these  teleseismic 
effects,  however,  is  still  far  from  complete,  and  the  settlement  of  the 
question  must  be  left  to  the  future. 

§  61.  Internal  state  of  the  earth. 

The   investigations   of  Lord   Kelvin  and   Professor   Sir   G.   H. 

1  In  his  "  Journal  of  Researches  during  the  Voyage  of  the  Beagle,"  1845, 
p.  291,  Charles  Darwin  mentions  this  remarkable  coincidence  of  phenomena: 
After  a  long  slumber,  Conseguina  in  Central  America,  and  Aconcagua  and 
Corcovado  (S.  lat.  32^°  and  43^2°)  in  Chile,  broke  out  the  same  day!  His 
suspicion  that  this  coincidence  was  not  accidental  would  be  confirmed  by 
our  knowledge  of  the  Andean  trough,  in  the  line  of  which  all  these  volcanoes 
are  situated. 


402  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

Darwin  have  shown  that  the  earth  is  highly  rigid,  and  in  a  recent 
paper  on  the  rigidity  of  the  heavenly  bodies  (cf.  Astron.  Nachr., 
No.  4104)  the  writer  has  shown  that  no  motion  of  currents  deep 
down  in  our  planet  is  really  possible,  because  of  the  enormous 
friction  due  to  the  pressure  at  great  depths.  Thus  no  currents  of 
fluids  or  gases  exist  in  the  earth,  except  just  under  the  crust  where 
the  explosive  strain  is  terrific.  And  even  near  the  surface,  where 
the  lava  is  forced  to  move  under  the  thin  crust,  in  the  building  of 
mountain  chains  like  the  Andes,  the  motion  is  usually  accomplished 
only  by  the  dreadful  paroxysm  of  an  earthquake,  which  expels  the 
molten  rock  from  under  the  bed  of  the  sea.  The  suspicion  of  Capt. 
Fitzroy  and  Charles  Darwin  that  in  the  three  months  following  the 
earthquake  of  1835  the  Chilean  coast  partially  subsided  to  its  former 
level  seems  not  only  possible,  but  extremely  probable.  Under  great 
strain  the  viscous  mass  may  have  yielded  somewhat,  and  thus  there 
may  have  been  a  slow  creeping  tendency  towards  the  former  level. 

Judging  by  the  thickness  of  the  sides  of  Aconcagua,  Cotopaxi 
and  other  typical  volcanoes  of  the  Andes,  one  would  probably  be 
justified  in  concluding  that  the  thickness  of  the  crust  under  which 
the  lava  moves  when  expelled  is  not  less  than  five  miles,  and  it  may 
be  as  much  as  fifteen  or  twenty,  but  ordinarily  it  could  not  well  lie 
outside  of  these  limits.  For  if.  we  suppose  it  to  be  thicker,  the  leak- 
age of  the  water  would  present  greater  difficulty  if  the  temperature 
is  low ;  and  such  thickness  would  not  be  required  if  adequate  steam 
developed  nearer  the  surface.  On  the  other  hand,  the  thickness 
could  hardly  be  much  less  than  ten  miles  without  enfeebling  the 
layers  which  must  support  great  strain  in  the  expulsion  of  matter 
from  the  broad  trough  of  the  ocean  bed.  The  most  probable  thick- 
ness is  from  ten  to  twenty,  and  for  most  purposes  we  shall  be  safe 
in  adopting  the  simple  mean  of  fifteen  miles. 

There  are  other  considerations  which  lead  to  substantially  the 
same  conclusion.  It  is  found  for  example  by  the  critical  investiga- 
tion of  great  earthquakes  that  most  of  these  disturbances  proceed 
from  an  average  depth  of  something  like  ten  to  fifteen  miles.  Now, 
if  the  theory  here  developed  be  admissible,  it  will  follow  that  these 
disturbances  usually  are  in  or  near  the  lower  stratum  of  the  earth's 
crust,  which  thus  fixes  the  thickness  of  the  layer  at  about  the  same 


19o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  403 

figure.  It  will  be  evident  from  this  consideration  and  others  that 
the  thickness  of  the  crust  is  by  no  means  uniform  throughout  the 
globe.  Determinations  of  the  depths  of  large  earthquake  disturbances 
are  probably  the  best  means  of  approximating  the  thickness  of  the 
earth's  crust,  since  data  of  this  kind  depend  wholly  upon  observation 
and  are  indepenedent  of  any  hypothesis. 

XII.     CONCLUSIONS. 
§  62.  Summary  of  results. 

,  i .  We  have  seen  that  deposits  of  sediment  on  the  continental 
shelves  could  not  possibly  produce  anything  but  the  most  gradual 
increase  of  weight  on  these  portions  of  the  earth's  crust;  and  since 
such  rocks  as  marble  are  proved  to  be  fluids  of  great  viscosity  and 
therefore  capable  of  slow  secular  bending  without  rupture,  we  may 
feel  sure  that  any  stresses  thus  arising  in  the  earth's  crust  would 
be  relieved  by  gradual  yielding,  and  that  no  violent  earthquake  shock 
could  ever  arise  from  such  a  cause. 

2.  The  theory  that  earthquakes  are  due  to  fracture  and  slipping 
of  rocks  is  disproved  by  the  great  depth    (ten  to  twenty  miles) 
at  which  world-shaking  earthquakes  are  found  to  originate,  and  by 
virtue  of  the  fact  that  they  come  not  from  a  point  nor  from  a  line, 
but  from  an  area;  and  moreover  earthquakes  follow  the  seashore, 
seldom  occurring  far  inland,  and  never  in  desert  countries,  though 
abundant  in  the  bed  of  the  ocean. 

3.  It  therefore  follows  that  earthquakes  must  depend  upon  ex- 
plosive forces  within  or  just  under  the  earth's  crust,  and  frequently 
spread  over  a  considerable  area,  and  the  preponderance  of  disturb- 
ances in  the  sea  and  along  the  shores  of  continents  shows  that  the 
forces  depend  in  some  way  upon  the  sea  water.     These  explosive 
forces  can  be  best  studied  in  connection  with  the  eruption  of  vol- 
canoes, since  volcanic  outbreaks  are  also  accompanied  by  earth- 
quakes often  felt  over  large  areas. 

4.  Not  all  earthquakes  lead  to  eruptions,  but  if  the  shocks  in  a 
given  region  cease  on  the  eruption  of  a  neighboring  volcano,  we  may 
feel  sure  that  the  forces  producing  the  eruption  also  produced  the 
antecedent  earthquake  shocks  felt  by  the  surrounding  country. 

5.  That  steam  is  the  cause  of  volcanic  eruptions  is  proved  by  the 


404-  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  i9r 

distribution  of  active  volcanoes  about  the  seashores  and  by  the 
innumerable  eruptions  which  occur  in  the  depths  of  the  ocean, 
whereas  such  vents  always  die  out  inland ;  and  moreover  by  the  fact 
that  of  the  vapors  emitted  from  volcanoes  999  parts  in  1,000  is 
estimated  to  be  steam,  the  remaining  one-thousandth  part  being  by- 
products incidental  to  the  moisture  and  high  temperature. 

6.  The  vera  causa  of  volcanic  action  and  of  certain  earthquakes 
thus  established  for  some  particular  cases  must  be  held  to  be  the 
universal  cause  in  all  cases  whatsoever,  according  to  Newton's  rule 
of  philosophy. 

7.  The  heaving  of  steam  accumulating  within  or  just  beneath 
the  earth's  crust  is  therefore  the  true  cause  of  all  world-shaking 
earthquakes,  and  volcanic  outbreaks  occur  only  when  an  outlet  is 
forced  through  to  the  surface,  which  usually  happens  in  mountains, 
where  the  earth's  crust  is  already  badly  fractured  and  upheaved. 

8.  When  the  subterranean  steam  pressure  becomes  great  enough 
to  shake  the  earth's  crust,  it  naturally  moves  at  the  nearest  fault  line, 
where  the  rocks  are  broken,  but  the  movement  observed  is  the  result, 
not  the  cause  of  the  earthquake. 

9.  Volcanoes   are   particular   mountains   blown   open   by   steam 
pressure  under  the  throes  of  earthquakes  (cracks  in  the  rocks  appear 
to  be  the  beginning  of  some  few  volcanoes),  and  since  all  volcanoes 
blow  out  pumice  and  ashes,  these  materials  must  be  held  to  exist 
in  all  mountains,  and  are  made  by  the  inflation  of  molten  rock  with 
steam  and  other  vapors. 

10.  Any  mountain  peak,   therefore,   is   capable   of  becoming  a 
volcano  if  the  subterranean  steam  pressure  be  sufficiently  powerful 
to  break  open  an  orifice.     But  orifices  close  up  and  volcanoes  die 
out  inland  and  elsewhere  if  the  supply  of  steam  is  inadequate  to 
keep  open  the  vents  upon   which  the  activity  depends.     Even  if 
stopped  up  for  a  time  later  heaving  of  the  earth  may  give  the  vol- 
cano renewed  activity,  and  when  the  mountain  has  been  dormant 
for  a  long  time  it  is  found  that  the  violence  of  the  eruption  is  greatly 
increased.    The  violence  of  the  subterranean  pressure  in  such  a  case 
approaches  that  of  a  region  which  has  no  vent  at  all,  and  hence  we 
see  why  earthquakes  in  non-volcanic  regions  frequently  become  so- 
terrible,  because  the  forces  accumulate  to  frightful  fury  before  any 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  405 

relief  whatever  is  afforded,  and  the  result  is  a  most  terrible  earth- 
quake. 

11.  The    mountains    are    formed    by    the    injection    of    steam- 
saturated  lava  under  the  coast,  which  breaks  the  overlying  surface 
rocks  and  gives  rise  to  a  ridge  parallel  to  the  sea.     This  is  why  all 
mountains  are  formed  parallel  to  the  seashores. 

12.  By  continually  injecting  the  land  with  lava  from  under  the 
bed  of  the  sea  the  coast  is  raised  and  the  mountains  upheaved,  and 
some  of  them  usually  break  out  into  volcanoes;  while  at  the  same 
time  the  support  of  the  sea  bottom  is  undermined  by  the  thinning 
out  of  the  fluid  substratum,  and  at  intervals  the  bottom  sinks  down 
to  restore  stability. 

13.  The  sinking  of  the  sea  bottom  in  this  natural  process  of 
earthquake  injection  of  the  land  is  the  cause  of  that  class  of  sea 
waves  found  to  follow  violent  earthquakes,  in  which  the  water  first 
withdraws  from  the  shore  and  then  returns  as  a  huge  wave.    Those 
waves  noticed  to  rise  suddenly  without  previous  recession  of  the 
water  usually  are  due  to  submarine  upheavals  and  eruptions  in  the 
bed  of  the  sea. 

14.  Islands  are  built  up  by  injection  from  the  sea,  and  hence 
have  their  mountains  as  veritable  backbones,  because  the  injection 
is  symmetrical  from  both  sides.     In  many  cases  the  sea  bottom  is 
thus  undermined  and  finally  sinks  down,  making  a  hole  beside  the 
island,  or  a  trench.     The  fact  that  all  islands  are  not  accompanied 
by  such  sinks  is  no  argument  against  the  theory,  because  the  subsi- 
dence has  not  always  taken  place ;  it  is  the  occurrence  of  even  a  con- 
siderable number  of  such  sinks  beside   islands   which  proves  the 
validity  of  the  theory.    Such  intimate  associations  between  elevation 
and  depression  could  not  be  the  result  of  chance. 

15.  In  the  repair  of  ocean  cables  broken  by  earthquakes,  Subsi- 
dence of  the  sea  bottom  is  frequently  found  to  follow  these  dis- 
turbances.   This  is  a  direct  observation  of  the  above  effects  in  certain 
cases  which  are  established  by  actual  measurement,  the  subsidences 
frequently  amounting  to  hundreds  of  fathoms. 

1 6.  The  sea  bottom  does  not  subside  without  the  lava  under  the 
crust  being  forced  out  into  some  other  place,  as  into  islands,  sub- 
marine ridges,   or  shores;  none  of  this  movement  is  due  to  the 


406  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

secular  cooling  of  the  earth,  but  is  all  to  be  explained  by  the  under- 
mining effect  of  steam  accumulating  under  the  earth's  crust. 

17.  Mountains  in  the  interior  of  a  dry  country,  as  the  Rocky 
Mountains   in   Colorado,   exhibit   no   important  movements,   while 
those  on  the  coast,  like  the  Andes,  are  always  heaving.    This  shows 
that  the  sea  is  the  cause,  and  not  the  secular  cooling  of  the  globe, 
which  is  wholly  insensible. 

1 8.  The  only,  countries  which  are  free  from  earthquakes  are  the 
deserts,  and  therefore  practically  uninhabitable ;  there  is  accordingly 
no  escape  from  earthquakes,  and  buildings  designed  for  permanency 
should  be  framed  to  withstand  them  without  material  injury. 

19.  While  in  the  long  run  the  elevation  of  the  land  predominates, 
there  is  also  subsidence,  due  to  the  non-concurrence  of  the  forces 
in  certain  regions  beneath  the  crust.    It  is  idle  to  deny  these  oscilla- 
tory movements  of  the  crust,  and  many  good  illustrations  of  both 
are  clearly  established.     Every  island  which  is  thrown  up  in  the 
sea  is  a  witness  to  one  of  the  most  general  laws  of  nature. 

20.  As  water  is  taken  up  in  the  crust  both  in  the  crystallization 
of  rocks  and  in  the  processes  of  earthquake  movements,  and  only  a 
part  of  this  vapor  is  restored  to  the  surface  through  volcanic  action, 
there  is  a  secular  desiccation  of  the  oceans,  but  the  process  is  exces- 
sively  slow   and   not  certainly   recognizable   during   the  historical 
period,  though  a  part  of  the  lowering  of  the  strand  line  in  later 
geological  ages  is  no  doubt  traceable  to  this  cause. 

21.  The  elevation  of  the  plateaus  depends  on  the  same  cause 
which  upheaved  the  mountains ;  and  all  plateaus,  like  the  mountains, 
are  underlaid  with  various   forms  of  pumice,  which  accounts   for 
their  feeble  attraction  as  shown  by  geodetic  observations. 

22.  No  doubt  various  chemical  changes  go  on  under  the  earth's 
crust  where  the  water  has  penetrated  the  lava  and  the  steam  becomes 
superheated,  but  the  predominance  of  water  vapor  in  volcanoes 
shows  that  the  other  gases  are  only  by-products,  incidental  to  the 
moisture  and  great  heat.    Dissociation  of  water  vapor  is  one  of  these 
effects. 

23.  The  details  of  mountain  structure  admit  of  explanation  on 
the  present  hypothesis,  while  heretofore  no  such  explanation  was 
forthcoming.     A   theorv   which   accounts   for  the  position   of  the 


19o6.]  SEE-THE  CAUSE  OF  EARTHQUAKES.  407 

ranges  relatively  to  the  sea,  the  slopes  of  the  ranges,  and  the  side 
spurs,  and  the  relation  of  mountains  to  earthquake  and  volcanic 
phenomena,  should  have  a  strong  claim  to  acceptance.  This  theory 
was  partially  foreshadowed  by  the  Arabian  astronomer  Avicenna,  in 
the  tenth  century  of  our  era. 

24.  The  theory  of  the  penetration  of  sea  water  into  the  crust 
of  the  earth  and  its  connection  with  volcanoes  and  earthquakes 
dates  back  to  Lucretius  and  Aristotle,  while  the  upheaval  of  the  land 
is  distinctly  announced  by  Strabo.  We  have,  therefore,  been  simply 
verifying  and  extending  the  impressions  of  the  ancients  formed 
from  the  general  aspects  of  nature  long  before  the  sciences  had 
become  exact.1 

§  63.  General  considerations. 

1  Since  finishing  this  paper  the  writer  has  been  much  impressed  with  the 
following  passage  in  the  article  Poseidon,  Encyclopedia  Britannica,  ninth 
edition : 

"  POSEIDON,  the  ancient  Greek  god  of  the  sea  and  of  water  generally.  .  .  . 
He  was  the  god  of  navigation,  adored  by  all  who  sailed  the  sea.  His  temples 
stood  especially  on  headlands  and  isthmuses.  As  god  of  the  sea  he  disputed 
with  other  deities  for  the  possession  of  the  land — with  Athene  for  Athens 
and  Troezen,  with  Helios  for  Corinth,  with  Hera  for  Argos,  with  Zeus  for 
Aegina,  etc.  Earthquakes  were  thought  to  be  produced  by  Poseidon  shaking 
the  earth, — hence  his  epithet  of  '  Earth-shaker,'  and  hence  he  was  worshipped 
even  in  inland  places,  like  Apamea  in  Phrygia,  which  had  suffered  from 
earthquakes,  flence  also  may  have  arisen  the  custom  in  some  places  of 
sacrificing  moles  to  him.  The  great  sea-wave  which  often  accompanies  an 
earthquake  was  also  his  work;  the  destruction  of  Helice  in  Achaia  by  such 
a  wave  (373  B.  C.)  was  attributed  to  his  wrath.  Once  when  an  earthquake 
shook  the  ground  where  a  Spartan  army  was  encamped,  the  whole  army 
sung  a  hymn  to  Poseidon.  The  island  of  Delos  was  thought  to  have  been 
raised  by  him  from  the  bottom  of  the  sea,  and  in  237  B.  C,  when  a  new 
island  appeared  between  Thera  and  Therasia,  the  Rhodians  founded  a  temple 
of  Poseidon  on  it.  Thessaly  was  said  to  have  been  a  lake  until  this  god 
opened  a  way  for  the  waters  through  the  Vale  of  Tempe.  Poseidon  was  also 
the  god  of  springs,  which  he  produced  by  striking  the  rock  with  his  trident, 
as  he  did  on  the  acropolis  of  Athens  when  he  was  disputing  with  Athene  for 
the  sovereignty  of  Athens.  This  dispute  was  represented  on  the  western  pedi- 
ment of  the  Parthenon.  .  .  .  There  were  collossal  statues  of  him  at  Helice 
in  Achaia,  on  the  Isthmus  of  Corinth  (set  up  by  the  Greeks  after  the  Persian 
wars)  and  at  Tenos." 

It  is  very  remarkable  to  find  that  at  an  early  age  the  Greeks  had  so 
directly  connected  earthquakes  with  the  sea,  probably  through  the  seismic 
sea  waves,  which  they  often  observed  in  this  part  of  the  Mediterranean. 
(Note  added  December  17,  1906.) 


408  SEE- THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

The  way  in  which  several  different  classes  of  phenomena  find 
explanation  by  the  most  simple  of  causes  may  be  considered  not  the 
least  remarkable  result  of  the  present  investigation.  In  the  minds 
of  those  who  follow  Newton's  first  rule  of  philosophy,  "  to  admit 
no  more  causes  of  natural  things  than  are  both  true  and  sufficient 
to  explain  their  appearances,"  this  will  probably  tell  strongly  in 
favor  of  the  truth  of  an  hypothesis  which  explains  easily  and  natur- 
ally such  diversified  phenomena  as  earthquakes  and  volcanoes,  the 
formation  of  mountains  and  the  deficiency  in  their  attractions,  the 
origin  of  cordilleras  from  the  ocean  trenches  near  continents,  and  of 
the  great  sea  waves  which  frequently  accompany  violent  earthquakes. 
But  there  will  doubtless  be  others  who  will  prefer  a  variety  of 
causes,  and  -will  be  slow  to  believe  that  the  laws  and  order  of  nature 
ire  so  simple. 

In  an  investigation  of  such  considerable  extent  it  would  not 
be  surprising  if  many  difficulties  should  require  further  elucidation 
than  they  have  received  in  this  imperfect  outline ;  for  the  writer  has 
not  the  geological  learning  required  for  the  full  treatment  of  many 
of  the  great  problems  of  the  earth's  crust.  But  if,  on  the  one  hand, 
some  defects  or  omissions  should  be  found,  and  no  doubt  many  of 
them  will  appear  in  special  branches  of  the  extensive  lines  of 
thought  here  traversed,  may  it  not  be  thought,  on  the  other,  that  the 
harmony  established  with  geodetical  measurements  on  the  attrac- 
tions of  mountains  and  the  deviations  of  the  plumb  line,  combined 
with  the  explanation  of  the  equilibrium  of  the  terrestrial  spheroid 
between  the  land  and  water  hemispheres,  is  not  wholly  without  a 
certain  degree  of  compensation  to  those  interested  in  the  numerous 
and  related  problems  of  the  physics  of  the  earth? 

That  the  existing  theory  of  earthquakes  and  volcanoes  and 
mountain  formation  is  embarrassed  by  many  difficulties  has  often 
been  frankly  admitted.  While  the  theory  here  suggested  may  re- 
quire extension  or  modification,  one  may  confidently  submit  the 
question  whether  it  is  really  possible  to  doubt  its  essential  truth.1 

1  The  sinking  of  the  sea  bottom  after  great  earthquakes  have  heaved  up 
the  coast,  as  along  the  west  shore  of  South  America,  furnishes  a  truly 
remarkable  criterion  for  unraveling  the  unseen  processes  of  nature,  hidden 
beneath  the  earth's  crust  The  sea  bottom  could  not  sink  unless  it  was  in 
some  way  undermined,  and  the  adjacent  coast  could  not  be  upraised  unless 


X9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES,  409 

If  this  inference  should  prove  to  be  well  founded,  may  it  not  be 
possible  to  conclude  the  contest  long  waged  between  astronomy  and 
geology  with  credit  and  advantage  to  both  of  these  great  sciences? 
For  it  seems  to  be  proved  that  owing  to  the  great  pressure  acting 
throughout  the  earth's  interior,  and  the  solidity  of  the  rocks  which 
cover  its  surface,  the  terrestrial  spheroid,  when  subjected  to  great 
strain,  behaves  and  vibrates  as  an  seolotropic  elastic  solid;  yet  the 
fluid  medium  long  contended  for  by  geologists  to  explain  crump- 
lings  and  foldings  of  the  crust  is  really  found  to  exist  or  develop  in 
a  thin  layer  just  beneath  the  outer  crust,  and  we  have  explained 
its  simple  and  somewhat  automatic  mode  of  operation.  On  several 
grounds  it  appears  that  this  layer  is  extremely  thin,  certainly  not 
much  thicker  than  the  crust  itself;  and,  moreover,  it  too  remains 
essentially  quiescent  and  rigid,  except  when  set  in  motion  by  the 
recurring  paroxysms  of  steam  pressure  seeking  release,  which  gives 
rise  to  an  earthquake  and  the  movements  of  molten  matter  essential 
to  geological  processes.  The  original  conceptions  of  astronomy  are 
thus  apparently  verified,  while  at  the  same  time  the  long-standing 
needs  of  geology  are  amply  met.  And  although  no  effort  has  been 
made  in  this  paper  to  harmonize  the  conflicting  views  long  prevailing 
in  the  two  sciences,  it  would  seem  that  this  unexpected  result  may 
prove  to  be  not  the  least  interesting  among  several  conclusions 
respecting  the  constitution  of  the  globe. 

something  was  pushed  under  it:  both  these  movements  are  observed  to 
occur,  and  always  in  the  same  order.  Along  the  shore,  just  parallel  to  the 
sea  coast,  the  crust  is  pushed  upward  to  form  mountains,  while  the  adjacent 
sea  bottom  is  correspondingly  sunk  down.  Can  anyone  doubt  that  we  have 
here  a  true  cycle  of  events?  One  of  these  events  necessitates  the  other,  and 
all  are  so  connected  that  one  can  begin  at  either  end  of  the  chain  of  phe- 
nomena and  reach  the  other.  Thus,  if  we  begin  with  volcanoes  we  are  led 
downward  through  these  vents  to  the  earthquake  and  mountain  forming 
forces  at  work  under  the  surrounding  land;  and  finally  we  come  out  beneath 
the  ocean  where  world-shaking  earthquakes  and  seismic  sea  waves  originate. 
On  the  other  hand,  if  we  begin  with  seismic  sea  waves,  we  are  led  downward 
through  the  observed  subsidence  of  the  sea  bottom  and  pass  under  the  crust 
to  the  mountains  raised  along  the  coast,  by  earthquakes  occurring  mainly 
under  the  sea,  and  thus  finally  reach  the  volcanoes  at  the  top  of  the  range, 
erupted  by  the  pressure  of  subterranean  steam,  and  blowing  out  lava,  pumice, 
ashes,  and  vapors.  All  the  grandest  phenomena  relating  to  the  earth's  sur- 
face are  thus  connected  in  an  endless  chain  or  circuit.  Could  such  perfect 
order  and  harmony  be  established  among  all  these  varied  phenomena  without 
the  discovery  of  the  true  physical  cause?  (Note  added  December  3,  1906.) 


410  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19 

The  details  of  the  processes  involved  in  the  elevation  of  conti- 
nents, and  just  how  these  great  land  areas  originated,  are  yet  to  be 
worked  out,  and  appear  to  be  involved  in  considerable  obscurity, 
most  probably  connected  with  the  terrestrial  origin  of  the  moon. 
Perhaps  our  knowledge  is  still  too  incomplete  for  a  satisfactory 
attempt  at  this  inquiry;  but  it  seems  not  improbable  that  the  lines 
of  thought  here  struck  out  may.  eventually  prove  fruitful  of  further 
discovery. 

§  64.  Origin  of  the  present  investigation. 

It  will  be  seen  from  the  foregoing  account  that  the  present  in- 
vestigation grew  out  of  the  difficulty  of  explaining  satisfactorily 
the  rotatory  motion  of  the  San  Francisco  earthquake.  When  the 
writer  very  soon  became  convinced  that  the  accepted  theory,  which 
explained  these  phenomena  by  dislocations,  subsidences  and  faults, 
was  not  well  founded,  the  investigation  was  extended  little  by  little 
till  it  covered  a  number  of  important  natural  phenomena  not  usually 
correlated.  The  order  in  which  this  extension  took  place  is  perhaps 
of  no  importance,  but  to  enable  anyone  who  might  be  curious  to 
understand  the  original  line  of  thought,  it  may  not  be  wholly  out  of 
place  to  mention  that  the  next  step  was  to  assign  the  explosive 
activity  of  volcanoes  to  steam;  and  then  the  traditional  reasoning 
about  these  vents  being  safety  valves  was  intelligible,  and  it  became 
clear  why  violent  earthquakes  do  not  predominate  in  volcanic  dis- 
tricts and  why  large  tectonic  earthquakes  are  always  so  violent. 

While  considering  the  mode  of  release  of  steam  pressure  in 
tectonic  earthquakes,  where  the  strata  are  unbroken,  I  was  led  to 
inquire  into  the  origin  of  mountains.  The  only  explanation  I  could 
find  was  by  the  theory  of  contraction  producing  folding  along  lines 
of  weakness  in  the  earth's  crust.  It  seemed  to  me  remarkable  that 
the  lines  of  weakness  should  nearly  always  follow  the  coast  lines 
of  continents.  Such  an  arrangement  should  not  occur  by  chance. 
It  was  easy  to  grasp  the  connection  of  earthquakes  with  volcanic 
activity  when  the  volcano  is  once  formed ;  and  the  question  naturally 
arose,  how  did  the  volcanoes  and  mountain  chains  originate?  I 
recalled  that  volcanic  islands  are  always  being  thrown  up,  and 
numerous  islands  had  been  formed  in  this  way  on  the  bed  of  the 
sea,  which  are  mountains  under  water.  On  the  other  hand  most 


I9o6.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  411 

geological  theories  regarded  the  mountains  as  formed  in  the  past, 
while  it  seemed  to  me  that  some  of  the  mountains  are  near  enough 
to  the  seashore  to  be  still  in  the  process  of  upheaval.  In  reflecting 
over  these  questions,  on  May  2Oth,  I  recalled,  from  impressions  ob- 
tained at  the  Coast  Survey  in  1899,  that  some  of  the  islands  in  the 
sea  had  depressions  on  the  side  of  them  as  if  the  material  had  been 
thrown  up  from  the  adjacent  bed,  and  that  deep  trenches  in  the 
oceans  also  ran  parallel  to  the  great  ranges  such  as  the  Andes.  I 
noticed  also  that  the  volume  of  the  Andes  and  of  the  islands  were 
severally  not  very  far  from  equal  to  those  of  the  adjacent  trough 
and  sinks.  Could  it  be  possible  that  the  Andes  also  had  been  raised 
by  matter  pushed  up  under  the  crust  from  the  bed  of  the  adjacent 
oceanic  trough?  On  recalling  that  the  sea  bottom  near  Pelee  has 
been  found  by  observations  to  have  actually  sunk  after  the  great 
ejection  of  ashes  and  vapors  in  1902,  and  that  the  hollow  form  of 
the  Andean  trough  would  prevent  vertical  eruptions  from  beneath, 
and  cause  any  explosions  which  might  originate  under  it  to  seek 
release  at  the  sides,  thus  pushing  up  the  mountains  through  col- 
umns or  rather  layers  of  lava  advanced  little  by  little,  by  "lateral 
thrusts,"  as  the  geologists  say,  from  under  the  sea,  I  did  not  hesitate 
to  conclude  that  the  Andes  had  originated  in  that  way.  The  ex- 
istence of  the  long  trough,  so  deep  and  so  exactly  parallel  to  the 
mountains  for  so  great  a  distance,  proved  it;  and  it  was  easy  to  see 
also  that  later  the  resistance  toward  the  land  side  would  become  so 
great,  owing  to  the  great  distance  and  height  of  the  mountains,  that 
release  would  eventually  come  more  easily  by  the  other  side  of  the 
trough  folding  up  into  a  parallel  range,  which  would  thus  emerge 
from  the  sea  as  the  New  Andes,  and  eventually  cause  a  further  re- 
cession of  the  west  coast  line  of  South  America. 

The  provisional  entertainment  and  private  acceptance  of  these 
views  seemed  daring  enough,  but  it  appeared  to  me  there  was  no 
escape  from  them.  On  the  following  day,  May  21,  I  recalled  that 
geodetic  observations  indicated  a  feebler  attraction  for  mountains 
than  if  they  were  solid  and  of  the  same  mean  density  as  the  crust ; 
and  it  was  evident  that  my  earlier  conception  of  pumice-filled  cones 
and  chains  had  not  been  altogether  too  rash.  The  rest  of  the  work 
consisted  in  nothing  but  verification  and  elaboration  of  these 
intuitions. 


412  SEE-THE  CAUSE  OF  EARTHQUAKES.  [October «,, 

Moreover,  the  cause  of  the  great  sea  waves  was  now  perfectly 
clear.  It  was  impossible  to  doubt  that  these  phenomena,  of  the 
class  in  which  the  water  recedes  from  the  shore  in  the  first  few 
minutes  following  an  earthquake,  generally  arise  from  a  subsidence 
of  the  sea  bottom  after  the  expulsion  of  porous  lava  in  the  natural 
process  of  elevating  the  mountains  and  coasts.  , 

After  these  ideas  had  been  worked  out  in  such  a  way  as  to  es- 
tablish harmony  among  the  widely  diversified  phenomena  it  was 
gratifying  to  find  that  such  views  were  not  inconsistent  with  the 
thoughtful  remarks  of  Humboldt,  and  that  Charles  Darwin  seventy 
years  before  had  reached  conclusions  in  most  respects  remarkably 
similar.  It  seemed,  therefore,  justifiable  to  suppose  that  the  process 
of  mountain  formation  thus  outlined  and  verified  was  in  all  proba- 
bility the  correct  one.  Such  was  the  order  of  the  writer's  thought, 
which  he  records  with  reluctance  and  hesitation,  but  chiefly  in  the 
hope  that  it  may  not  be  wholly  without  value  to  others. 

In  the  final  arrangement  of  the  paper  it  was  deemed  best  to  intro- 
duce the  citations  from  Humboldt  and  Darwin  under  the  discussion 
of  the  several  topics  rather  than  as  extremely  long  foot-notes.  And 
this  arrangement  was  the  more  agreeable  on  account  of  the  great 
esteem  in  which  the  writer  has  always  held  these  illustrious  investi- 
gators. As  Professor  Milne  is  justly  recognized  to  be  the  most 
eminent  living  authority  on  earthquakes,  to  whom  we  owe  extensive 
international  cooperation  and  the  present  widespread  interest  in  the 
subject,  which  has  contributed  so  greatly  to  the  advancement  of  our 
knowledge,  the  same  principle  has  naturally  been  employed  in  the 
exposition  of  the  results  of  his  researches. 

While  it  is  impossible  to  estimate  too  highly  the  great  strides 
recently  made  in  seismology  under  the  leadership  of  Professor 
Milne,  Dr.  Davidson,  Montessus  de  Ballore,  Major  Dutton,  Von 
Rebeur-Paschwitz,  Dr.  Agamennone,  Dr.  Rudolph,  Professor 
Omori,  and  others,  who  have  reduced  seismology  to  a  science  of 
precise  observation  and  measurement,  it  is  perhaps  unfortunate  that 
the  views  of  Humboldt  and  Charles  Darwin  as  to  the  causes  involved 
in  earthquakes  were  ever  abandoned  by  modern  investigators,  though 
this  probably  has  not  retarded  the  progress  of  observation  and 
experimentation  on  the  constitution  of  the  globe. 


1906.]  SEE— THE  CAUSE  OF  EARTHQUAKES.  413 

In  certain  respects  the  theory  here  outlined  may  be  capable  of 
observational  tests.  The  importance  of  the  subject  would  appear 
to  be  such  that  it  may  be  worthy  of  consideration  whether  geodetic 
investigators  of  the  different  nations  might  not  advantageously 
arrange  to  establish  earthquake  and  tidal  observatories  and  more 
precise  levels  on  coasts  such  as  those  of  Chili,  Peru,  California,  Japan, 
Italy,  Greece  and  other  countries,  for  the  more  exact  study  of  pro- 
gressive secular  movements.  Has  not  the  time  come  to  test  geo- 
logical and  seismological  theories  by  the  accumulation  of  exact 
empirical  data,  and  is  not  this  a  debt  which  we  of  this  generation 
owe  to  the  future  ? 

§  65.  Seismic  activity  a  maximum  along  the  coasts  of  deep  seas 
and  a  minimum  in  the  great  inland  deserts. 

If  the  cause  assigned  for  the  explanation  of  earthquakes  be 
confirmed  by  time  and  experience,  it  is  evident  that  no  place  on 
the  earth  can  be  said  to  be  wholly  removed  from  the  danger  of  these 
disturbances;  yet  the  dangers  will  be  a  maximum  on  the  coasts  of 
deep  seas  where  the  shores  are  of  leaky  character  and  the  troughs 
are  at  work,1  and  grow  less  and  less  along  the  coasts  of  the  shallower 
waters  where  the  troughs  are  absent  and  the  stratification  of  the 
rocks  is  more  secure.  Thus  northern  and  central  Europe  and  the 
eastern  coast  of  the  United  States  are  comparatively  safe.  Yet 
sooner  or  later,  but  fortunately  to  be  reckoned  in  many  cases  by 
intervals  of  thousands  of  years,  every  place  (except  the  great  in- 
land deserts  which  are  nearly  uninhabitable)  is  likely  to  be  shaken 
by  an  earthquake  of  considerable  severity;  and  those  works  of  man 
which  are  to  be  preserved  and  to  stand  through  the  centuries  should 
be  built  accordingly.2  The  great  layer  of  water  covering  the  earth, 

1  In  his  thoughtful  article  on  "  Geology,"  Encyc.  Brit.,  p.  255,  Sir  Archibald 
Geikie  justly  remarks:  "Some  of  the  most  terrible  earthquakes  within  human 
experience  have  been  those  which  have  affected  the  western  seaboard  of  South 
America."      The  cause  of  this   is  now   plain,   viz.,   the   Andean   Trough   is 
probably  the  largest  and  most  powerful  in  the  world.      And  in  general  the 
seimicity  of  a  region  in  the  production  of  world-shaking  earthquakes  depends 
on  the  extent  and  power  of  its  ocean  troughs. 

2  Humboldt  laments  the  destruction  wrought  by  earthquakes  upon  works 
of  art,  architecture,  monuments  and  inscriptions  of  the  classic  period,  which 
were  developed  in  a  region  of  such  high  seismic  activity  as  to  render  their 
preservation  difficult. 


414  SEE— THE  CAUSE  OF  EARTHQUAKES.  [October  19, 

which  gives  life  to  animals  and  plants,  and  in  the  form  of  steam  is 
the  greatest  mechanical  agent  of  man,  when  sunk  into  the  crust  be- 
comes also  one  of  his  worst  destroyers,  on  account  of  the  explosive 
vapor  generated  beneath  by  the  internal  heat  of  the  globe. 

Finally,  it  may  not  be  without  interest  to  note  that,  so  far  as  our 
knowledge  extends,  the  earth  alone  among  the  encrusted  planets 
of  the  solar  system  has  an  abundance  of  water  and  mountains,  with 
volcanoes  and  earthquakes.  Mars  seems  to  have  only  a  trace  of 
water  and  no  sensible  mountains  or  volcanoes.  And  while  Venus 
is  largely  obscured  from  our  view,  the  chances  are  that  its  veil  is 
due  to  clouds,  indicating  an  abundance  of  water,  and  hence  that  its 
conditions  of  evolution  may  approach  those  of  the  earth. 

BLUE  RIDGE  ON  LOUTRE,  MONTGOMERY  CITY,  MISSOURI, 
September  23,  1906. 

NOTE. — For  kind  permission  to  use  Figs.  6,  7,  8,  and  9  we  are 
indebted  to  the  courtesy  of  Rand,  McNally  and  Co.,  of  Chicago. 


LD  21-40m-10,'65 
(F7763slO)476 


General  Library 

University  of  California 

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